Marine and Freshwater Resources Institute
Report No. 39
Seagrass Mapping of Port Phillip Bay
Sean Blake and David Ball
June 2001 Marine and Freshwater Resources Institute
Report No. 39
Seagrass Mapping of Port Phillip Bay
Sean Blake and David Ball
June 2001
Marine and Freshwater Resources Institute PO Box 114 Queenscliff 3225 © The State of Victoria, Department of Natural Resources and Environment, 2001
This work is copyright. Apart from any use under the Copyright Act 1968, no part may be reproduced by any process without written permission.
ISSN: 1328-5548
ISBN: 0 7311 4995 5
Copies available from: Librarian Marine and Freshwater Resources Institute PO Box 114 Queenscliff VIC 3225 Phone: (03) 5258 0259 Fax: (03) 5258 0270 Email: [email protected]
Preferred way to cite this publication: Blake, S. and Ball, D. (2001). Victorian Marine Habitat Database: Seagrass Mapping of Port Phillip Bay. Geospatial Systems Section, Marine and Freshwater Resources Institute Report No. 39. Marine and Freshwater Resources Institute: Queenscliff.
General disclaimer: This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. Seagrass Mapping of Port Phillip Bay
CONTENTS
List of Figures ...... ii List of Tables...... ii List of Historical Photographs...... ii List of Appendices ...... iii
SUMMARY...... 1
1. INTRODUCTION ...... 2
1.1 Objectives...... 2 1.2 Seagrass...... 2 1.3 Port Phillip Bay...... 3 1.4 Seagrass Species in Port Phillip Bay...... 5
2. MAPPING THE SPATIAL DISTRIBUTION AND DENSITY OF SEAGRASS IN PORT PHILLIP BAY...... 7
2.1 Survey Methods...... 7 2.1.1 Remote Sensing of Shallow Marine Environments...... 7 2.1.2 Photography Specifications...... 7 2.1.3 Aerial Photography Interpretation...... 7 2.1.4 Field Verification Process ...... 7 2.1.5 Field Classifications ...... 9 2.2 Results of Mapping...... 15 2.3 Discussion...... 17 2.4 Assessment of Mapping...... 19
3. AN ASSESSMENT OF SEAGRASS CHANGES IN PORT PHILLIP BAY...... 21
3.1 Previous Studies ...... 21 3.1.1 Bay-wide Studies...... 21 3.1.2 Site-specific studies...... 22 3.2 Comparison of Previous Studies with 2000 Mapping...... 24 3.3 Assessment of Seagrass Changes from Historical Aerial Photography 30 3.3.1 Selection of Study Sites and Aerial Photography ...... 30 3.3.2 Scanning and Geo-registration of Historical Aerial Photography ...... 30 3.3.3 Results...... 31 3.3.4 Observations from Historical Aerial Photography ...... 31 3.3.5 Summary of Observations from Historical Aerial Photography ...... 33 3.4 Overview of Assessing Seagrass Changes with Historic Aerial Photography...... 34
4. GENERAL DISCUSSION AND FINDINGS ...... 38
ACKNOWLEDGMENTS ...... 39
Marine and Freshwater Resources Institute – Page i Seagrass Mapping of Port Phillip Bay
REFERENCES...... 40
LIST OF FIGURES
Figure 1.1 Port Phillip Bay location map Figure 2.1 Specialised survey vessel with semi submersible pod lowered Figure 2.2a Ground-truthing transects and points recorded in Port Phillip Bay Figure 2.2b Example of how the fieldwork transects were used to classify the mapping derived from aerial photography. Figure 2.3 Seagrasses of Port Phillip Bay Figure 2.5 Areas of individual seagrass categories as a percentage of the total area of seagrass mapped in Port Phillip Bay Figure 3.1a Seagrass distribution in Port Phillip Bay, 1957, 1962-63 Figure 3.1b Seagrass distribution in Port Phillip Bay, 1968-70 Figure 3.1c Seagrass distribution in Port Phillip Bay, 1978-81 Figure 3.1d Seagrass distribution in Port Phillip Bay, 2000 Figure 3.2a Area of seagrass cover as a percentage of total study area at Grassy Point Figure 3.2b Area of seagrass cover as a percentage of total study area at Sands Caravan Park site, Leopold Figure 3.2c Area of seagrass cover as a percentage of total study area at Altona Figure 3.2d Area of seagrass cover as a percentage of total study area at Blairgowrie Appendix 3 Figure 2.4 Seagrass map index Appendix 3 Figures 2.4a-p Maps of seagrass distribution in Port Phillip Bay
LIST OF TABLES
Table 2.1 Seagrass and macroalgae species and density and substrate classification categories recorded during the field survey Table 2.2 Summary area statements for seagrass and macroalgae categories recorded in Port Phillip Bay Table 2.3 Results of a points-in-polygons analysis - groundtruthing versus seagrass polygons. Table 3.1 Areas of seagrass recorded in Port Phillip Bay (Bay-wide studies) Table 3.2 Results of historic studies compared to present study Table 3.3 Historical aerial photography used to identify changes in seagrass distribution at specific sites in Port Phillip Bay
LIST OF HISTORICAL PHOTOGRAPHS – APPENDIX 2
Photo 3.1a Grassy Point, 1947 (Scale 1:10,000) Photo 3.1b Grassy Point, 1975 (Scale 1:10,000) Photo 3.1c Grassy Point, 1992 (Scale 1:10,000) Photo 3.1d Grassy Point, 2000 (Scale 1:10,000) Photo 3.2a Sands Caravan Park, Leopold, 1974 (Scale 1:10,000) Photo 3.2b Sands Caravan Park, Leopold, 1984 (Scale 1:10,000) Photo 3.2c Sands Caravan Park, Leopold, 1993 (Scale 1:10,000)
Marine and Freshwater Resources Institute – Page ii Seagrass Mapping of Port Phillip Bay
Photo 3.2d Sands Caravan Park, Leopold, 2000 (Scale 1:10,000) Photo 3.3a Altona, 1962 (Scale 1:10,000) Photo 3.3b Altona, 1979 (Scale 1:10,000) Photo 3.3c Altona, 1993 (Scale 1:10,000) Photo 3.3d Altona, 2000 (Scale 1:10,000) Photo 3.4a Blairgowrie, 1966 (Scale 1:10,000). Photo 3.4b Blairgowrie, 1993 (Scale 1:10,000). Photo 3.4c Blairgowrie, 1996 (Scale 1:10,000). Photo 3.4d Blairgowrie, 2000 (Scale 1:10,000).
LIST OF APPENDICES
Appendix 1 Seagrass GIS Layer Metadata ...... A1 Appendix 2 Port Phillip Bay Historical Aerial Photography...... A10 Appendix 3 Port Phillip Bay Seagrass Maps...... A19
Important Note on Seagrass Species Definition
The two species of Zosteraceae observed in Port Phillip Bay; Heterozostera tasmanica and Zostera muelleri, cannot be differentiated by the remote sensing techniques employed in this study and have been grouped into a single category of “Zostera/Heterozostera”.
Marine and Freshwater Resources Institute – Page iii Seagrass Mapping of Port Phillip Bay
SUMMARY
This study forms part of a state-wide program by the Department of Natural Resources and Environment (NRE) to map and characterise the distribution of seagrass communities throughout Victoria. The objectives of the study were to map the distribution of the different seagrass species found in Port Phillip Bay and to compare the present distribution with that observed in previous studies.
The mapping method involved acquiring high quality aerial photography, interpreting the aerial photography to identify seagrass areas, ground-truthing these areas in the field, digitising seagrass areas with a GIS and adding seagrass species and density attributes for each area based on the field data. The fieldwork was primarily undertaken by running transects with a specialised survey vessel equipped with a semi-submersible pod, or by taking spot samples from a small punt or from the shore.
Four species of seagrass were recorded during the survey; Zostera muelleri, Heterozostera tasmanica, Halophila australis and Amphibolis antarctica. The two species of Zosteraceae, Heterozostera tasmanica and Zostera muelleri, could not be differentiated by the remote sensing techniques employed in this study and as a result were grouped into a single category of “Zostera/Heterozostera”. Several different categories of macroalgae were also recorded (Caulerpa, Codium and Ulva being recorded to genus level and Phyllospora comosa/Ecklonia radiata to species level), although most were classified in the generic category “Undefined Macroalgae”. The ascidian Pyura stolonifera was also mapped.
The present study mapped a total vegetated area of 169.4 km2 (seagrass, macroalgae and Pyura) in Port Phillip Bay of which, 67.99 km2 or 40% was seagrass or a mixture of seagrass and algae. The dominant category of all vegetation by area was “Undefined Macroalgae” which accounted for an area of 85.37 km2 or 50% of the total vegetation mapped. The remaining 10% consisted of different categories of algal species and Pyura.
Zostera/Heterozostera (representing a mix of Zostera muelleri and Heterozostera tasmanica) was the dominant category of seagrass recorded in the Bay accounting for 59.3 km2 or 95% of the total seagrass mapped. A. antarctica accounted for 3% of the total seagrass mapped and H. australis accounted for the remaining 2%.
The majority of Zostera/Heterozostera was recorded in Swan Bay and along the southern shores of the Geelong Arm and Corio Bay. Significant areas were also present along the north shores of Corio Bay and the Geelong Arm, south of St. Leonards (West Sand Bank), around Mud Islands (Great Sand), off Sorrento (South Sand) and along the Rosebud to Blairgowrie foreshore. Smaller isolated patches were scattered around the Bay, with very little along the eastern shores. A. antarctica was restricted in its distribution to Point Lonsdale Bay, north to Queenscliff Pier and along the shore from Point Nepean to Sorrento. H. australis was restricted to the deeper, soft sediments of Swan Bay, the Geelong Arm and Corio Bay
Comparisons of the present mapping survey with past mapping projects and research indicate little by way of large-scale change in the overall distribution of seagrass in Port Phillip Bay since 1957. A review of quantitative data derived from an assessment of historical aerial photography supports the pattern of a relatively consistent Bay-wide distribution of seagrass with frequent localised small-scale changes over short periods of time.
Marine and Freshwater Resources Institute – Page 1 Seagrass Mapping of Port Phillip Bay
1. INTRODUCTION
This study forms part of a state-wide program by the Department of Natural Resources and Environment (NRE) to map and characterise the distribution of seagrass communities throughout Victoria. The seagrass mapping program is being conducted by the Marine and Freshwater Resources Institute (MAFRI) and mapping has already been completed for the Gippsland Lakes (Roob & Ball 1997), Corner Inlet and Nooramunga (Roob et al. 1998), the Eastern Minor Inlets (Blake et al. 2000) and Western Port (Blake & Ball 2001). Port Phillip Bay was the final area to be mapped as part of the program.
Seagrass mapping will provide ecological information towards an improved understanding of seagrass distribution and diversity, its role in commercial and recreational fisheries as well as baseline data for future environmental monitoring. The results of this study will also be integrated with The Environmental Inventory of Victoria’s Marine Ecosystems, a multi-stage project to provide information on the diversity of marine ecosystems at various spatial scales (Ferns and Hough 1999).
This report is divided into two sections, with the first presenting the results of a seagrass mapping program undertaken in Port Phillip Bay and the second presenting an assessment of changes in seagrass distribution in recent times. The first section details the spatial extent, species distribution and density of seagrass beds determined through the application of remote sensing techniques and field verification. The second section presents the results of an assessment of seagrass changes in Port Phillip Bay through a comparative review of previous mapping studies and a quantitative assessment of historical aerial photography.
1.1 Objectives
The objectives of the study are to:
1. Map the spatial extent of seagrass in Port Phillip Bay.
2. Identify the distribution of seagrass species in Port Phillip Bay.
3. Undertake a comparison of the present seagrass distribution in Port Phillip Bay with that observed previously.
1.2 Seagrass
Seagrasses are aquatic angiosperms. Their internal structures and reproductive strategies all show particular adaptations to a completely aquatic existence. Seagrasses have extensive horizontal underground stems (rhizomes) and strong roots that anchor the plant to the soft bottom (Lloyd 1997). The roots absorb nutrients, but do not take up water. To cope with living in oxygen-poor mud, seagrasses have evolved air canals that carry oxygen from the leaves to the buried rhizomes and roots. Erect branches and leaves grow off the buried stem. The leaves have a thin skin that allows efficient nutrient and gas uptake from the water (Lloyd 1997).
Marine and Freshwater Resources Institute – Page 2 Seagrass Mapping of Port Phillip Bay
Typically, seagrass meadows are found in water depths of 2-12 metres where sunlight intensity is greatest and therefore seagrass growth is highest, although some species are adapted to the intertidal zone (Lloyd 1997). The photosynthetic activity of seagrass beds can be sufficient to cause significant changes in oxygen, carbon dioxide and acidity levels of the surrounding water (Lloyd 1997).
Seagrasses are colonisers of mud, silt and sand, using their extensive rhizome systems to anchor them and consequently stabilising the sediments. The leaves also impede currents increasing sedimentation around the plants. Seagrasses are important for water quality, helping to maintain low concentrations of suspended solids, silicate and phosphorus.
Seagrass is an ecologically significant marine habitat that is both highly productive and provides food and shelter for many organisms. Small animals are able to shelter among the seagrass leaves, protected from predators and from excessive sunlight or temporal changes in salinity and temperature (Hastings 1995). Seagrass meadows provide food for benthic fauna and scavenger communities living in the mudflats and these in turn provide food for fish, crustaceans, birds and waterfowl. Many organisms receive nutrients from seagrass detritus, either directly or indirectly. Some animals feed directly on the seagrass, such as Black Swans, while others graze on epiphytes or seagrass detritus.
Seagrass meadows provide ideal habitats for fish, with much research indicating they play an important role as nursery areas for the juvenile stages of certain species. Jenkins et al. (1997) compared fish assemblages of seagrass habitats with fish assemblages of unvegetated habitats in different areas of Victoria. It was found that diversity was higher in seagrass meadows than in unvegetated areas. The larval stages of some fish species, such as blue rock whiting, King George whiting, six-spine leatherjacket and rough leatherjacket, settled directly on deeper, subtidal Heterozostera tasmanica beds, with adult rock flathead and juvenile luderick also favouring seagrass sites. Flounder, while favouring unvegetated habitats, are thought to benefit from organic enrichment of sediments by seagrass debris due to increased food production (Shaw & Jenkins 1992, and Jenkins et al. 1993 in: Jenkins et al. 1997). In general, the biomass and abundance of fish were greater in subtidal seagrass habitats than in unvegetated subtidal habitats.
1.3 Port Phillip Bay
Port Phillip Bay is located on the central south coast of Victoria. It is a large, shallow marine embayment with an area of 1,950 km2, a 260 km long coastline and a narrow entrance to Bass Strait, between Port Phillip Heads, known as The Rip (Figure 1.1). The Rip is 3.2 km wide at high tide.
With the exception of The Rip, which reaches depths in excess of 90 m, the majority of Port Phillip Bay is relatively shallow (<25 m – Figure 1.1). Of the total volume, approximately half is in waters shallower than 8 m, and of the total surface area of the bay, approximately half is less than 14 m deep (Harris et al. 1996 in: Light & Beardall 1998).
Marine and Freshwater Resources Institute – Page 3 Seagrass Mapping of Port Phillip Bay
Port Phillip Bay is believed to be a drowned river system (Keble 1946 in: Hope Black 1971) and the contours of the former valley are reflected in the present day bathymetric contours. The northern part of the bay is a saucer-shaped basin with a maximum depth of 24 m, while the southern part is shallow, with extensive shoals exposed at low tide between deeper tidal channels that converge towards Port Phillip Heads (Jones 1980 in: Bird 1993). Swan Island and Mud Island are also located in this southern region.
Tides in Port Phillip Bay are semi-diurnal, generally with a range of less than 1m. Average tidal variations range from 0.9 m at Williamstown, at the entrance to the Yarra River, to 1.7 m at Point Lonsdale at the Bay entrance (Victorian Channels Authority Web Site 2000). “The hydrodynamics are characterised by an entrance region where fast (3 m s -1) ebb and flood jets dominate the circulation, a large flood-tidal delta known as The Sands region, where strong currents occur in the major channels, and an inner zone where tidal currents are weak” (Black et al. 1993). The average tidal exchange through The Rip is approximately 1 km3, or 4% of the Bay’s total volume (Vic. Govt. 1992 in: Winstanley 1995). On the western side of the Bay, near the entrance to the Geelong arm, tidal currents are reduced to below 10 cm s-1 (Jenkins & Wheatley 1998). There is a time-lag of over 3 hours between high tide at Port Phillip Heads and high tide in Williamstown and Corio to the north due to the Bay’s narrow entrance and the barrier presented by the Great Sands.
Sediments ranging from clays to gravels account for approximately 90% of the substrate in Port Phillip Bay. The remaining 10% consists of reefs (Hope Black 1971). These broad substrate types are an important influence on the distribution of flora and fauna within the Bay. Macroalgal communities are generally associated with areas of reef, and form the dominant floral community around the Heads region of the Bay. Mangroves, salt flats/salt marsh and seagrasses are all present in the Bay.
The Bay’s catchment area is estimated at 9,780 km2, of which 21% is uncleared land, 18% is developed for urban use, 1% for industrial uses and 60% for agriculture (Saenger & Bucher 1989). Each year the Bay receives 1.4 km3 of fresh water from its surrounding catchment, plus 1.2 km3 of rainwater, 0.2 km3 of treated sewage effluent and an estimated 40,000 tonnes of sediment from the Yarra River (Light & Beardall 1998).
Shipping channels run through the Bay from Port Phillip Heads to the major ports of Melbourne and Geelong. The Port of Melbourne is the largest container port in Australia, and Geelong is an important import and export bulk port. The Victorian Channels Authority Annual Report (1999) states that a total of 3,338 vessels visited the Geelong and Melbourne ports in 1997/98 and 3,542 visited in 1998/99.
As well as being very important as a recreational destination for fishing, boating, sightseeing and related tourism, Port Phillip Bay also supports a large commercial fishery. Figures for the commercial catches of the main species in 1997/98 quoted a total catch of 1,089 tonnes, representing a value of over $2.7 million (Fisheries Victoria 1998).
Marine and Freshwater Resources Institute – Page 4 Seagrass Mapping of Port Phillip Bay
N Melbourne
Shippi ng W E channel
S
Werribee
Corio Geelong PORT Bay Arm PHILLIP Shippi ng BAY channel Portarlington Frankston Geelong Swan Bay Depth (m) Land Queenscliff 0-5 05-10 10-15 15-20 The Rip 20-25 10 0 10 20 Kilometers Rosebud 25 +
Figure 1.1 Port Phillip Bay location map
1.4 Seagrass Species in Port Phillip Bay
There are 55 species of seagrasses in the world with 25 occurring in Australia. According to Harris et al. (1996) eight species of seagrass have been recorded in Port Phillip Bay. The dominant species are Zostera muelleri, Heterozostera tasmanica (both belonging to the Family Zosteraceae), Halophila australis (Family Hydrocharitaceae), and Amphibolis antarctica (Family Cymodoceaceae) (Figure 2.3). Earlier reports cite Heterozostera tasmanica as Zostera tasmanica, A. antarctica as Cymodocea antarctica and possibly Halophila australis as H. ovalis (refer to the note at end of this section regarding the classification of Halophila).
In addition to the four main species listed above, species of the genera Ruppia and Lepilaena (families Potamogetonaceae and Zannichelliaceae, respectively) have also been recorded in Port Phillip Bay, primarily in Swan Bay. Robertson (1984 in: Womersley 1984) notes that these two genera frequently grow in close association, are characterised by being tolerant to a wide range of salinities and are not generally recognised as seagrasses. The species reported in Swan Bay include Lepilaena marina, Lepilaena cylindrocarpa, Ruppia maritima, Ruppia tuberosa and Ruppia polycarpa (DCE 1991).
Bulthuis (1981) reported seagrasses occurring mainly in the southern half of the Bay, around Port Phillip Heads, in Swan Bay, Corio Bay and the Geelong Arm. Small
Marine and Freshwater Resources Institute – Page 5 Seagrass Mapping of Port Phillip Bay isolated patches were also recorded along the eastern and northern shores. H. tasmanica was found to be the dominant species at most of the sites studied, occurring from the intertidal zone to depths of approximately 9 m. Higher in the intertidal zone Z. muelleri was dominant and was common in Swan Bay. H. ovalis (syn. H. australis) was generally found below H. tasmanica as a fringing band in the sublittoral zone.
Growth of A. antarctica is restricted to the areas around Port Phillip Heads, where the sediments are coarse and sandy and wave and current energy is at its strongest.
Note: Classification of Halophila In the report, Literature and Information Review of the Benthic Flora of Port Phillip Bay (Light & Woekerling 1992), several papers were cited as recording Halophila ovalis in Port Phillip Bay, in particular Swan Bay. However, the Swan Bay Marine and Wildlife Reserves Proposed Management Plan (DCE 1991) records Halophila australis as being present in Swan Bay. This, combined with Edgar (1997) and Robertson (1984 in: Womersley 1984) both stating the distribution of H. ovalis as being tropical and H. australis as temperate, would indicate that H. australis is actually the species present in Port Phillip Bay.
Marine and Freshwater Resources Institute – Page 6 Seagrass Mapping of Port Phillip Bay
2. MAPPING THE SPATIAL DISTRIBUTION AND DENSITY OF SEAGRASS IN PORT PHILLIP BAY
This section details the spatial extent, species distribution and density of seagrass meadows recorded in Port Phillip Bay through the application of remote sensing and field verification techniques.
2.1 Survey Methods
The survey methodology employed in this study is consistent with the previous surveys undertaken as part of the statewide seagrass mapping program (see Roob & Ball 1997, Roob et al. 1998, Blake et al. 2000 and Blake & Ball 2001).
2.1.1 Remote Sensing of Shallow Marine Environments
Aerial photography was chosen as the most effective method of remotely sensing the spatial extent of seagrass meadows in Port Phillip Bay at the pre-determined scale of 1:25,000. In order to accurately determine the spatial extent of seagrass it was essential that the photography be flown when optimum conditions existed to maximise light penetration through the water column. Cloud free days, during a period of calm weather with low rainfall and on a low tide were the primary considerations.
2.1.2 Photography Specifications
Colour aerial photography was flown at a scale of 1:20,000 which could then be reproduced at 1:10,000 for the final interpretation, without compromising detail. Photography for the study was flown on the 25th and 31st of March 2000, and on the 2nd and 3rd of April 2000.
2.1.3 Aerial Photography Interpretation
Colour contact prints of the aerial photography were printed as double size, full frame enlargements (ie. 1:10,000). The boundaries of all potentially vegetated areas were visually interpreted from these photographs and drafted onto stable base polyester sheets overlaying the photography. This line-work was then scanned and a raster to vector conversion carried out to produce a digital version of the seagrass boundaries. The digital data was then converted to a GIS format and edited with the GIS software ARCINFO.
2.1.4 Field Verification Process
In order to ground-truth the interpretation of vegetated areas from the aerial photography, a field program was designed to conduct transects and, if necessary, spot samples throughout the Bay. The selection of areas to be surveyed was determined directly from the aerial photography and from preliminary maps produced from the
Marine and Freshwater Resources Institute – Page 7 Seagrass Mapping of Port Phillip Bay initial interpretation of the photography. Geographic coordinates for areas to be surveyed and "way points" were identified to assist in navigating to seagrass sites in the field. Draft maps produced from the interpretation of the aerial photography, as well as the photographs themselves, were taken into the field to assist in locating areas to be surveyed.
Water clarity was generally good in Port Phillip Bay and with the exception of certain areas such as Swan Bay, Limeburner’s Bay and Kororoit Creek, access was generally suitable for the use of a specialised survey vessel with a semi-submersible observation pod (Fig 2.1). In areas where the water depth was too shallow for the specialised survey vessel, a small flat-bottomed aluminium punt was utilised. Certain areas of the Bay had to be navigated with caution due to the presence of shallow reefs.
Figure 2.1 Specialised survey vessel with semi submersible observation pod lowered
The specialised survey vessel (Figure 2.1) was fitted with a Differential Global Positioning System (DGPS). An observer sat in the lowered semi-submersible pod and viewed the subtidal vegetation through glass plates incorporated in the pod. Using a hand-held computer connected to the DGPS, the observer selected pre-defined "hot- keys" to record seagrass and other vegetation types present, the density of vegetation and where visible, the substrate type. The system records positional data from the DGPS and the seagrass observations every 5 seconds, producing continuous transects composed of individual data points. The distribution of transects conducted in Port Phillip is shown in Figure 2.2a. Figure 2.2b shows how the data derived from the fieldwork is used in conjunction with the aerial photography to classify seagrass areas.
Where shallow water depths prevented transecting with the specialised survey vessel, a small punt was used to collect “spot samples” (in very shallow areas, spot samples were recorded by wading out from the shore). A portable DGPS system was again used to record accurate positional fixes and an observer used a glass-bottomed tube to identify subtidal vegetation types, vegetation densities and substrate types at each spot check site. The location of spot sample sites is also shown in Figure 2.2a.
Marine and Freshwater Resources Institute – Page 8 Seagrass Mapping of Port Phillip Bay
2.1.5 Field Classifications
Species: Four species of seagrass were recorded during the survey; Zostera muelleri, Heterozostera tasmanica, Halophila australis and Amphibolis antarctica (Figure 2.3). The two species of Zosteraceae, Heterozostera tasmanica and Zostera muelleri, cannot be differentiated by the remote sensing techniques employed in this study and as a result were grouped into a single species category of “Zostera/Heterozostera” (Table 2.1).
Macroalgae or non-seagrass vegetation categories were also recorded during the survey and these are presented in Table 2.1. Where specific species of macroalgae were clearly dominant over an area, an attempt was made to record these to species level (Table 2.1). In cases where this was not possible, either due to poor visibility or no one species being clearly dominant, a category of “Undefined Macroalgae” was used.
Areas dominated by the ascidian Pyura (generally Pyura stolonifera also known as Cunjevoi or sea squirt) were also recorded during the survey.
Amphibolis antarctica often grows in and around areas of rocky reef and is commonly interspersed amongst the associated macroalgae. As a result it can be difficult to distinguish the density of A. antarctica, or to clearly define boundaries between it and associated areas of macroalgae using the mapping techniques and at the scale of mapping employed in this study. Consequently A. antarctica could not always be mapped as a separate species and a mixed category of “Amphibolis & Undefined Macroalgae Mix” was also used (Table 2.1).
Density: A visual assessment of seagrass density was recorded using categories of “Sparse”, “Medium” and “Dense”, representing:
· For “Zostera/Heterozostera” and “Amphibolis”:
Dense: Thick enough to hide the sediment underneath from view. Medium: Thick enough for leaves to touch but sediment could be discerned beneath. Sparse: When plants are present but of a density where leaves from individual plants essentially do not touch each other.
· For “Halophila”:
Dense: The base sediment could always be seen, but the leaves were within touching distance of each other. Medium: Present but leaves do not touch although within proximity of each other. Sparse: Leaves do not touch and individual plants clearly dispersed.
The same principles were applied to the estimation of algal densities (Table 2.1). Density was also directly interpreted from the aerial photography through the "darkness" of vegetated areas and the amount of seabed visible through the vegetated areas.
Marine and Freshwater Resources Institute – Page 9 Seagrass Mapping of Port Phillip Bay
Substrate Type: The primary purpose of recording substrate type was to differentiate between areas of sediment and areas of reef. Where reef was recorded, a category of “High Profile Reef” (relief of >1m above surrounding bed) or ‘Low Profile Reef” (relief of <1m above surrounding bed) was used. Where no significant algal growth was present on these reefs a category of “Bare Reef” was also used (this classification refers solely to vegetation cover and does not include invertebrate cover). In areas where reef was very broken and interspersed amongst sediment a category of “Sediment/Low profile Reef” or “Sediment/High Profile Reef” was used (Table 2.1).
Table 2.1 Seagrass and macroalgae species (including Pyura) and density and substrate classification categories recorded during the field survey. Classification Categories Attributes Species (Figure 2.1.) Zostera/Heterozostera (Heterozostera tasmanica and/or Zostera muelleri) Zostera/Heterozostera & Halophila Mix Zostera/Heterozostera & Caulerpa Mix Zostera/Heterozostera & Filamentous Algae Mix Zostera/Heterozostera & Undefined Macroalgae Mix Amphibolis Amphibolis & Undefined Macroalgae Mix Halophila & Filamentous Algae Mix Codium Dominant Macroalgae Phyllospora/Ecklonia Dominant Macroalgae (Phyllospora comosa and Ecklonia radiata) Caulerpa Dominant Macroalgae Ulva & Caulerpa Dominant Macroalgae Undefined Macroalgae Drift Algae Pyura (generally Pyura stolonifera) Pyura & Macroalgae Mix (generally Pyura stolonifera) No Visible Bottom (unable to discern biota)
Density Sparse Medium Dense
Substrate Type Sediment Low Profile Reef (relief < 1m) High Profile Reef (relief >1m) Sediment/Low Profile Reef Sediment/High Profile Reef Bare Reef (only refers to algal cover) Undefined (unable to discern bottom type)
Marine and Freshwater Resources Institute – Page 10 Seagrass Mapping of Port Phillip Bay
Figure 2.2a Ground-truthing transects and spot sample points recorded in Port Phillip Bay.
Marine and Freshwater Resources Institute – Page 11 Seagrass Mapping of Port Phillip Bay
Figure 2.2b Example of how the fieldwork transects were used to classify the vegetated areas interpreted from aerial photography. Site shown is Clifton Springs.
Marine and Freshwater Resources Institute – Page 12 Seagrass Mapping of Port Phillip Bay
Figure 2.3 Seagrasses of Port Phillip Bay a) Heterozostera tasmanica H. tasmanica is generally subtidal and exists where exposure to the atmosphere is limited. It occurs predominantly on sand and mud sediments.
H. tasmanica has an almost identical leaf shape to Zostera muelleri. It can sometimes be separated from other species on the basis of its branching pattern, with the leaves having dark wiry bases that arise vertically from the rhizomes, whereas the leaves of Zostera muelleri are often curved parallel with Heterozostera tasmanica (source G. Edgar) sediment near their bases (Edgar 1997). b) Zostera muelleri Z. muelleri generally exists in the intertidal zone, preferring sand and mud sediments, and requires extended periods of exposure to the atmosphere to survive.
Zostera muelleri has at least two roots at each node: the leaf apex is usually notched in the centre, and the leaf blade has three longitudinal veins. The only reliable way to separate these two species of Zosteraceae is to observe a cross-section of the rhizome with a Zostera muelleri (source B. Fuhrer) hand-lens or microscope. Heterozostera tasmanica has four to twelve vein-like vascular bundles arranged in a circle, whereas Zostera muelleri has only two (Edgar 1997). c) Halophila australis H. australis is subtidal and often associated with H. tasmanica, but growing on the deeper margins. This species is generally associated with softer muddier sediments.
H. australis has ovate leaves with stalk- like petioles. These arise from branched stems called stolons that lie half-buried in the sand (Edgar 1997). Halophila australis (source G. Edgar)
Marine and Freshwater Resources Institute – Page 13 Seagrass Mapping of Port Phillip Bay
d) Amphibolis antarctica A. antarctica is subtidal and generally restricted to areas with coarse sediments and increased water movement.
A. antarctica has woody, branched stems arising at irregular intervals from the rhizome. The stems are very tough and wiry. Leaves are small relative to the stems, flat with smooth margins, and have a blunt apex with two marginal teeth. The leaves are grouped in Amphibolis antarctica (source G. Edgar) clusters of eight to ten, and are twisted through 180º (Edgar 1997).
Marine and Freshwater Resources Institute – Page 14 Seagrass Mapping of Port Phillip Bay
2.2 Results of Mapping
The distribution of seagrass and macroalgae mapped in Port Phillip Bay by this study is presented in Figures 2.4a-p (Appendix 3). Table 2.2 provides a total area summary for each of the vegetation categories recorded during the study as well as the Pyura categories. The bar graph in Figure 2.5 shows the areas of the seagrass categories only (Zostera/Heterozostera, Amphibolis and Halophila) as a percentage of the total area of seagrass mapped in Port Phillip Bay.
Table 2.2 Summary area statements for seagrass, macroalgae and Pyura categories recorded in Port Phillip Bay. Vegetation Categories Area (m2) Area (km2) Seagrass and Seagrass and Macroalgae Mixed Categories Sparse Zostera/Heterozostera 11,022,092 11.02 Medium Zostera/Heterozostera 15,270,125 15.27 Dense Zostera/Heterozostera 5,425,274 5.43 Sparse Zostera/Heterozostera & Halophila Mix 181,930 0.18 Medium Zostera/Heterozostera & Halophila Mix 294,633 0.29 Sparse Zostera/Heterozostera & Caulerpa Mix 3,583,970 3.58 Medium Zostera/Heterozostera & Caulerpa Mix 885,915 0.89 Sparse Zostera/Heterozostera & Filamentous Algae Mix 17,295,562 17.30 Medium Zostera/Heterozostera & Filamentous Algae Mix 9,618,496 9.62 Dense Zostera/Heterozostera & Filamentous Algae Mix 662,617 0.66 Sparse Zostera/Heterozostera & Undefined Macroalgae Mix 108,793 0.11 Medium Zostera/Heterozostera & Undefined Macroalgae Mix 167,586 0.17 Dense Zostera/Heterozostera & Undefined Macroalgae Mix 13,814 0.01 Sparse Amphibolis 608,583 0.61 Medium Amphibolis 1,069,132 1.07 Dense Amphibolis 25,383 0.03 Sparse Amphibolis & Undefined Macroalgae Mix 179,754 0.18 Medium Amphibolis & Undefined Macroalgae Mix 203,873 0.20 Sparse Halophila & Filamentous Algae Mix 729,243 0.73 Medium Halophila & Filamentous Algae Mix 638,254 0.64 Dense Halophila & Filamentous Algae Mix 8,607 0.01 Sub-total area of seagrass categories only 67,993,637 67.99
Macroalgae and Pyura Categories Codium Dominant Macroalgae 35,723 0.04 Phyllospora/Ecklonia Dominant Macroalgae 638,554 0.64 Caulerpa Dominant Macroalgae 10,401,530 10.40 Ulva & Caulerpa Dominant Macroalgae 86,790 0.09 Undefined Macroalgae 85,370,175 85.37 Drift Algae 329,792 0.33 Pyura 315,148 0.32 Pyura & Macroalgae Mix 4,233,216 4.23 Sub-total area of Macroalgae and Pyura categories only 101,410,929 101.41 Total area of all vegetation categories 169,404,566 169.40
Marine and Freshwater Resources Institute – Page 15 Seagrass Mapping of Port Phillip Bay
30
25.44 25 22.46
20
16.21
15 14.15
% Cover of Seagrass 10 7.98
5.27 5
1.57 1.30 0.97 0.90 1.07 0.94 0.27 0.43 0.16 0.25 0.02 0.04 0.26 0.30 0.01 0
Dense Amphibolis Sparse AmphibolisMedium Amphibolis
Dense Zostera/Heterzostera Sparse Zostera/HeterozosteraMedium Zostera/Heterozostera
Dense Halophila & Filamentous Algae Mix Sparse HalophilaMedium & Filamentous Halophila & Algae Filamentous Mix Algae Mix Sparse Zostera/HeterozosteraMedium Zostera/HeterozosteraSparse & Halophila Zostera/HeterozosteraMedium Mix & Halophila Zostera/Heterozostera Mix & Caulerpa Mix & Caulerpa Mix Sparse AmphibolisMedium & Undefined Amphibolis Macroalgae & Undefined Mix Macroalgal Mix
Dense Zostera/Heterozostera & Filamentous Algae Mix Sparse Zostera/HeterozosteraMedium Zostera/Heterozostera & Filamentous &Algae Filamentous Mix Algae Mix Dense Zostera/Heterozostera & Undefined Macroalgae Mix Sparse Zostera/HeterozosteraMedium Zostera/Heterozostera & Undefined Macroalgae & Undefined Mix Macroalgae Mix
Figure 2.5 Areas of individual seagrass categories as a percentage of the total area of seagrass only mapped in Port Phillip Bay
Marine and Freshwater Resources Institute – Page 16 Seagrass Mapping of Port Phillip Bay
2.3 Discussion
A total area of 169.4 km2 of seagrass, macroalgae and Pyura was recorded in Port Phillip Bay during the present survey (Table 2.2). Of this, 67.99 km2 (40%) was recorded as being either seagrass or a mixture of seagrass and macroalgae. The dominant category of vegetation by area was Undefined Macroalgae, accounting for an area of 85.37 km2 or 50% of the total vegetation mapped. The remaining 10% consisted of macroalgae categories and Pyura (Table 2.2).
The dominant seagrass categories recorded were Zostera/Heterozostera, which covered 31.72 km2 for all density types, and Zostera/Heterozostera & Filamentous Algae Mix which covered 27.58 km2 for all density types (Table 2.2). Together, these categories accounted for 91.5% of the total area of seagrass mapped in Port Phillip Bay (Figure 2.5). The largest areas within the seagrass only categories were, Medium Zostera/Heterozostera which covered 15.27 km2 (22.46% of seagrass) and Sparse Zostera/Heterozostera & Filamentous Algae Mix which covered 17.3 km2 (25.44% of seagrass)
Amphibolis antarctica, with its preference for coarser sediments and higher energy environments, was the dominant species of seagrass recorded in the Port Phillip Heads region (Figures 2.4a & o – Appendix 3). No A. antarctica was recorded north of Queenscliff or east of Portsea (Point King). A. antarctica was often found growing on the sediments amongst areas of broken reef, and mixed with species of macroalgae.
Zostera/Heterozostera began to appear growing on the sediments in association with A. antarctica around the Police Point area at Portsea and the Dog Beach area at Lonsdale Bight (Figures 2.4a & o) and was the dominant seagrass category in Port Phillip Bay beyond The Heads region.
The majority of Swan Bay had some seagrass coverage (Figure 2.4a). The main exceptions to this was an area at the southern end of the Bay and an area near the centre of the Bay where Undefined Algae was the dominant vegetation category (Figure 2.4a). The southern half of Swan Bay was generally dominated by sparse Zostera/Heterozostera, which had filamentous algae associated with it. The northern half of Swan Bay had a far greater cover of medium to dense Zostera/Heterozostera with less filamentous algae. Halophila australis was also recorded mixed with the Zostera/Heterozostera in deeper water around the Swan Bay Jetty area (Figure 2.4a).
Seagrass distribution between Edwards Point and Portarlington was generally restricted to a narrow band of discontinuous patches running parallel to the coast in the nearshore zone (Figures 2.4b & c). A large area of Zostera/Heterozostera was present offshore on the West Sand Bank, east of Coles Channel. Seagrass cover increased significantly to the west of Point Richards with Zostera/Heterozostera being present from the intertidal zone to about the 5m depth contour (Figure 2.4c). At Clifton Springs the Zostera/Heterozostera was present mixed with undefined species of Caulerpa (Figures 2.4c & d).
Some of the highest seagrass leaf biomass in Port Phillip Bay was found between Clifton Springs and Point Henry and in particular the area between Seabrae Caravan
Marine and Freshwater Resources Institute – Page 17 Seagrass Mapping of Port Phillip Bay
Park and the Alcoa Pier (Figures 2.4d & e). In this area the Zostera/Heterozostera was not only dense in terms of cover but is also very long. The Zostera/Heterozostera north of Point Henry decreased in density and was mixed with H. australis on the deeper eastern margins. Stingaree Bay, west of Point Henry, was generally covered with Zostera/Heterozostera, although predominantly of a sparse to medium density (Figure 2.4e).
In Corio Bay, the coast between Limeburners Point and Corio Quay was characterised by two seagrass categories (Figure 2.4e). Zostera/Heterozostera (generally with filamentous algae) was found in the shallower waters from the shore to a depth of approximately 3-5m, with H. australis becoming dominant in the deeper water and where sediments were generally finer.
Sparse to medium Zostera/Heterozostera with filamentous algae was found in most of Limeburners Bay and along the entire northern shore of the Geelong Arm (Figures 2.4d & e). A bed of H. australis dominates the stretch of coast from Point Lillias to Snake Island. The coast from Point Lillias to Point Wilson also featured large areas of bare reef.
A band of sparse Zostera/Heterozostera with filamentous algae extended along the near shore for approximately 2 km north of Point Wilson before being replaced by a much broader band of Undefined Macroalgae (Figures 2.4d & f). Only small isolated patches of Zostera/Heterozostera were present from The Spit to Werribee South and were generally a mixture of seagrass and undefined species of Caulerpa (Figures 2.4f & g). No seagrass was recorded between Werribee South and Point Cook (Figures 2.4g & h). A large expanse of Undefined Algae, extending distances of up to 5 km offshore, dominated the region from Kirk Point to Point Cook (Figures 2.4f-h).
Sparse and medium patches of Zostera/Heterozostera began to reappear in the nearshore between Point Cook and Kororoit Creek, while large expanses of Undefined Algae continued to be the dominant vegetation category in the deeper waters (Figures 2.4h & i). Pyura beds and macroalgae extended from Point Cook to Altona (Figure 2.4h). Areas of bare high profile reef are the dominant nearshore habitat east of Kororoit Creek to the Breakwater Pier at Williamstown (Figure 2.4i).
No subtidal vegetation of any type was recorded between the Breakwater Pier at Williamstown and St. Kilda harbour, where areas of sparse-dense Zostera/Heterozostera with filamentous algae were observed in the harbour (Figure 2.4i). Only small isolated areas of Zostera/Heterozostera were present south of St. Kilda Pier to Table Rock Point, Beaumaris. Areas of seagrass could be observed near the entrance to St. Kilda Marina and in and around Point Cole, Sandringham Pier, Half Moon Bay and Ricketts Point (Figures 2.4i & j). Bare reef and reef with undefined algae dominated this length of coast.
A long sandy shore with very few subtidal features dominates the coast between Table Point Rock and Daveys Bay (Figures 2.4k & l). Bare reef and reefs with undefined algae were present south of Daveys Bay to Dromana Bay (Figures 2.4l & m). Almost no seagrass was recorded between Table Point Rock, Beaumaris and Rosebud Pier, with the exception being some sparse beds of Zostera/Heterozostera recorded in Dromana Bay (Figure 2.4m).
Marine and Freshwater Resources Institute – Page 18 Seagrass Mapping of Port Phillip Bay
Inshore beds of Zostera/Heterozostera were present in the nearshore zone from Rosebud Pier through to Portsea, where they begin to appear mixed with A. antarctica (Figures 2.4n &o). Zostera/Heterozostera beds were also present offshore across the South Sand region, the Great Sand region, at South Channel Fort and in and around Mud Islands (Figures 2.4n-p). Pyura beds were found with macroalgae around the South Channel Pile Light and offshore from Sorrento (Figure 2.4o).
2.4 Assessment of Mapping
The successful differentiation of seagrass and macroalgae species and relative densities through aerial photography interpretation is dependent on adequate ground-truthing data. Stephens (1995) noted for example, that a macro-algal epiphyte on the stems of much of the H. tasmanica in the lower North Arm of Western Port gave these areas a browner appearance on the aerial photography, which without adequate ground-truthing could have been misinterpreted as a lower seagrass density. For the purposes of ground-truthing the present study recorded approximately 450km of transect data, as well as several individual spot samples.
In an attempt to provide some measure of accuracy or ‘confidence’ in the present study’s mapping, a points-in-polygons analysis was carried out in ArcView to identify the proportion of mapped polygons that had been ground-truthed (Table 2.3). Of a total 2,902 polygons attributed with seagrass and non-seagrass classifications during the mapping, 47% contained at least one ground-truthing point. However, this 47% of sampled polygons represents over 81% or 257 km2 of the total area of seagrass and non- seagrass mapped during the study (excluding areas of “No Visible Bottom”). Such a result would indicate a high level of accuracy in the classification of species type and density in the mapping.
Marine and Freshwater Resources Institute – Page 19 Seagrass Mapping of Port Phillip Bay
Table 2.3 Results of a points-in-polygons analysis – ground-truthing versus seagrass polygons.
Total number of polygons mapped 2902.00 Total number of polygons mapped with at least one ground truthing point within them 1364.00 Therefore the % of polygons with points in them = 47.00%
Area (m2) Area (Km2) Total area mapped (Including "No Visible Bottom" (NVB) polygons) 1,936,772,590.21 1936.77
Total area of "NVB" polygons mapped 1,621,777,210.05 1621.78
Total area mapped (Excluding "NVB" polygons) 314,995,380.16 315.00
Total area mapped with points in the polygons (Including "NVB") 1,878,305,716.64 1878.31
Total area of "NVB" mapped with points in the polygons 1,621,498,763.79 1621.50
Total area mapped with points in the polygons (Excluding "NVB") 256,806,952.86 256.81
Therefore the % area of polygons with points in them (excluding "NVB") = 81.53%
Note: NVB = "No Visible Bottom" category
Marine and Freshwater Resources Institute – Page 20 Seagrass Mapping of Port Phillip Bay
3. AN ASSESSMENT OF SEAGRASS CHANGES IN PORT PHILLIP BAY
The following section presents a literature review of previous studies addressing seagrass in Port Phillip Bay and includes an assessment of seagrass changes in the Bay through a review of both previous mapping and historical aerial photography at selected sites.
3.1 Previous Studies
An extensive literature review of previous seagrass research was undertaken by Light and Woelkerling (1992) as part of the CSIRO Port Phillip Bay Environmental Study and the findings of this review are summarised below. Additional seagrass work undertaken in the Bay since the 1992 review is also outlined below. A summary of the main studies is given in Table 3.2.
3.1.1 Bay-wide Studies
Of the 34 Port Phillip Bay seagrass reference sources identified by Light and Woelkerling (1992) only five dealt with Bay-wide distributions of seagrass.
Willis (1966) addressed seagrass distribution in the Bay using data from the 1957-63 Port Phillip Survey. He identified four species of seagrass; Zostera muelleri, Heterozostera tasmanica (syn. Zostera tasmanica), Halophila Australis (syn. Halophila ovalis) and Amphibolis antarctica (syn. Cymodocea antarctica). Whilst Z. muelleri was described as being more common than H. tasmanica, a map presented in Willis (1966) grouped the two species of Zosteraceae as Zostera. However, an undated report by Brown (in: Light & Woelkerling 1992) later declared that all samples of Z. muelleri from Corio Bay, identified by Willis as Z. muelleri, were in fact H. tasmanica.
Willis (1966) described the distribution of Z. muelleri and H. tasmanica as being densest around the northern and southern shores of Corio Bay, in Swan Bay and from Swan Bay to Indented Head, with sparse occurrences observed at Mud Island, Rye, Werribee Estuary and Altona. Very little seagrass was recorded along the eastern shore of the Bay. An estimate of 47 mi2 (76 km2) was given for the total cover of Z muelleri and H. tasmanica in the Bay. Halophila was estimated to cover a far smaller area, with its distribution mainly confined to the western coast of the Bellarine Peninsula where it forms deeper bands fringing Caulerpa and Zostera beds. Amphibolis was restricted to small patches in the region around The Heads.
Bulthuis (1981) utilised field data and aerial photography collected during 1978-81 to map the distribution of seagrass in Port Phillip Bay (Figure 3.1c). This data was also used to assist in interpreting historic aerial photography to enable maps of the Bay-wide distribution of seagrass to be produced for the periods 1957/1962-63 and 1968-70 (see Figures 3.1a-b). A map of the Corio Bay and Swan Bay regions only was produced for the period 1947-50. While local variations in seagrass distribution had occurred Bulthuis (1981) stated that there had been no major changes in the general distribution of seagrasses in Port Phillip Bay since 1957-63.
Marine and Freshwater Resources Institute – Page 21 Seagrass Mapping of Port Phillip Bay
Bulthuis (1981) recorded the same four seagrass species as Willis (1966) but found H. tasmanica to be the most abundant species. Apart from this, his distribution of species generally reflects that of Willis (1966), with seagrasses occurring mainly in the southern portion of the Bay, around Corio Bay, the Geelong Arm, Swan Bay and Port Phillip Heads. Z. muelleri was prevalent higher in the littoral zone with H. tasmanica dominant in deeper, more turbulent but clear water, while H. ovalis (syn. H. australis) generally formed a fringing band below the H. tasmanica. Amphibolis antarctica was restricted to the areas of high water turbulence and sandy substrate associated with The Heads. Bulthuis (1981) concluded that of the estimated 110 km2 area of seagrass in 1978-81, 95% was in depths of less than 5m.
Hope Black (1971), utilised data collected on benthic fauna in Port Phillip Bay between 1957 and 1963 to make some observations on seagrass distribution within the Bay. He recorded Zostera beds on the sand in Capell Sound and the eastern shores of the Bellarine Peninsula, and on the silty/clay sands of Swan Bay and Corio Bay. These beds were often fringed on the seaward side by Cymodocea antarctica (syn. Amphibolis antarctica) and Halophila ovalis in the deeper channels (it is possible that the A. antarctica described in this report is actually H. tasmanica).
King et al. (1971) only studied species of seagrass from the intertidal zone in Port Phillip Bay. They recorded Zostera muelleri from numerous areas in the Bay, and Amphibolis antarctica from around The Heads region. King et al. (1971) also recorded two further species, Ruppia maritima and Lepilaena cylindrocarpa in Swan Bay. However, subsequent investigation of the work by King et al. (1971) found these two species to be referable to Ruppia tuberosa and Lepilaena marina respectively (Shepherd & Robertson 1989 in: Light & Woelkerling 1992).
3.1.2 Site-specific Studies
The remaining Port Phillip Bay seagrass studies cited by Light and Woelkerling (1992) focus on specific areas of the Bay. Some of these works are outlined below as well as other more recent studies.
Point Lonsdale Bight A survey of the subtidal environment in Point Lonsdale Bight by Marine Science and Ecology (1997) identified several major habitat types, while the bed of the Bight was described as being primarily a mix of low reef interspersed with well sorted fine to medium-coarse sands. Amphibolis antarctica was recorded as one of the dominant vegetation types in Lonsdale Bight forming extensive dense meadows. Small, localised patches of H. tasmanica were recorded in sheltered areas and some very sparse patches of H. australis were also recorded.
Swan Bay and Queenscliff Harbour Kerr (1983 in: Light & Woelkerling 1992) and Denning et al. (1986 in: Light & Woelkerling 1992) mapped the distribution, and estimated the biomass of Z. muelleri, H. tasmanica and H. ovalis (syn. H. australis) in Swan Bay. Kerr also recorded the presence of L. cylindrocarpa and Ruppia species.
Marine and Freshwater Resources Institute – Page 22 Seagrass Mapping of Port Phillip Bay
Ball & O’Callaghan (1997) found regions of Z. muelleri on intertidal sand/mud flats around Queenscliff Harbour to be extensive and dense (>25% cover). Areas of H. tasmanica were also recorded, generally on the subtidal flats and deeper channels.
A 1991 Department of Conservation and Environment draft management plan reported Z. muelleri and H. tasmanica communities in Swan Bay. Z. muelleri occurred as either mono-specific stands on intertidal flats or mixed with Lepilaena marina on the upper margins of the intertidal zone. Z. muelleri/L. marina communities were recorded along the western margins of Duck Island, Swan Island and along the southern shoreline. Ruppia maritima and Ruppia tuberosa were also recorded. H. tasmanica occurred intermixed with Z. muelleri at its upper limits and was also mixed with Halophila australis in the deeper channels (although H. australis was generally found in the north west of the Bay). Halophila decipiens was also recorded in Swan Bay (DCE 1991).
Several studies have investigated relationships between seagrass communities and various fish communities in Swan Bay and around the Bellarine Peninsula (see Jenkins et al. 1996, Jenkins et al. 1997, Saunders 1997 and Jenkins & Wheatley 1998).
Corio Bay Seedsman and Marsden (1980 in: Light & Woelkerling 1992) reported that seagrasses were primarily restricted to depths of less than 2 m in Corio Bay. Brown et al. (1980 and undated in: Light & Woelkerling 1992) described the distribution of H. tasmanica as being greatest in 2-3m depth, becoming patchy and associated with H. ovalis (syn. H. australis) in deeper water.
Marine Science and Ecology (1998) monitored the impacts on seagrass of a channel deepening program in the Geelong Arm. While H. tasmanica was the primary species targeted and recorded, Halophila australis was also observed at some sites. The report indicates minimal direct impacts on the seagrass from the dredging, but observed decreases in seagrass biomass which coincided with increased algal biomass. Decreases in algal biomass at some sites coincided with increased turbidity as a result of the dredging activity and may have actually lead to an increase in the seagrass biomass.
Werribee – Point Cook Brown et al. (1980 in: Light & Woelkerling 1992) found that seagrasses are generally rare in the Werribee region, but mono-specific stands of H. tasmanica occur at Kirk Point and the Murtcaim Drain.
Willis (1966 in: Light & Woelkerling 1992) and Spencer (1970 in: Light & Woelkerling 1992) recorded H. tasmanica beds occurring 5 km offshore from Point Cook and 1.5 km north of the mouth of Skeleton Creek, offshore from Altona.
St. Kilda Harbour A 1987 study by Marine Science and Ecology (Watson 1987) recorded two discrete and permanent areas of H. tasmanica in St. Kilda Harbour; one in the central Harbour area, and another in the south eastern corner. The standing crop of these areas was reported
Marine and Freshwater Resources Institute – Page 23 Seagrass Mapping of Port Phillip Bay to vary considerably over the years. A later survey by Greilach et al. (1998) mapped the extent of H. tasmanica in St. Kilda Harbour. Although figures for standing crop are not given it would appear from the map that there had been an increase in the area of seagrass in the Harbour. The report also reported the presence of H. tasmanica in the inner harbour at Brighton Boat Harbour and Sandringham Boat Harbour.
Mornington Peninsula Parry and Collett (1985) utilised historical aerial photography to investigate the distribution of H. tasmanica along the Rosebud-Rye foreshore. They found a marked increase in the amount of seagrass in the nearshore area between 1960 and 1981 and attributed this increase to the loss of sandy spits and transverse sand-bars as a result of beach renourishment dredging.
General Bulthuis and Woelkerling (1983) reported that growth of H. tasmanica in Port Phillip Bay (Edwards Point) generally follows a unimodal seasonal pattern, with maximum leaf standing crop, leaf cluster density and leaf productivity during the summer months. Kerr (1986 in: Ball & O’Callaghan 1997) and Kerr & Strother (1990 in: Ball & O’Callaghan 1997) reported that Z. muelleri also demonstrates a distinct annual cycle, with its above ground biomass during summer being 40 times greater than that in the winter months. Watson (1979 in: Light & Woelkerling 1992) reported on the standing crop of H. tasmanica at Point Richards Bank, between Point Richards and Spray Farm Road.
Bulthuis et al. (1992) reported that during the spring and summer months in Port Phillip Bay H. tasmanica growth was generally limited by nitrogen levels in the interstitial water of the sediments.
3.2 Comparison of Previous Studies with 2000 Mapping
The results of the current study have been compared with some of the past research outlined in the previous section. A summary of the past seagrass mapping and studies in Port Phillip Bay versus the present mapping is presented in Table 3.2.
Willis (1996) and Bulthuis (1981) recorded the same species of seagrass in Port Phillip Bay as the present study. The seagrass distribution recorded in the present study (Figure 3.1d) is also generally consistent with Willis (1996) and Bulthuis (1981) who recorded the largest areas of seagrass (Zostera and Heterozostera) within Port Phillip Bay at Corio Bay and the Geelong Arm, Swan Bay and Port Phillip Heads.
Willis (1966) reported H. australis as being restricted to the western coast of the Bellarine Peninsula, while the present study only found H. australis in Swan Bay, the Geelong Arm and Corio Bay. The present study and Willis (1966) and Bulthuis (1981) all recorded A. antarctica as being restricted to The Heads region.
Bulthuis (1981) produced Bay-wide maps of seagrass distribution for the periods 1957/1962-63 (Figure 3.1a), 1968-70 (Figure 3.1b) and 1978-81 (Figure 3.1c). A
Marine and Freshwater Resources Institute – Page 24 Seagrass Mapping of Port Phillip Bay simplified map showing the distribution of seagrass recorded by the present study is shown for comparison (Figure 3.1d). Area statements for the total area of seagrass recorded in Port Phillip Bay by the different mapping studies are presented in the following table.
Table 3.1 Areas of seagrass recorded in Port Phillip Bay (Bay-wide studies). Report Mapping Period Total area of Seagrass (km2)
Willis 1966 1957-63 76 Bulthuis 1981 1957, 1962-63 41* (does not include Portarlington to Indented Head or Mud Islands) Bulthuis 1981 1968-70 37* (does not include northern and central Swan Bay or Mud Islands) Bulthuis 1981 1978-81 96* (although the report states 110) Blake and Ball 2001 2000 68 *Maps produced by Bulthuis were subsequently digitised with a GIS by CSIRO during the Port Phillip Bay Environmental Study and the areas stated here have been determined from this digital data.
It should be noted that some of the variation in the distribution of seagrass (Figures 3.1a-d), and consequently the area statements (Table 3.1), is due to the extent of photography available for that period rather than actual changes in seagrass distribution. For example, no seagrass was mapped between Portarlington and St Leonards and at Mud Islands in 1957, 1962-3 (Figure 3.1a) or in Swan Bay and Mud Islands for 1968-70 (Figure 3.1b) as there was no aerial photography available for these areas. The seagrass area value for 1978-81 may also be an overestimate, as while no ground-truthing was undertaken in the area, Bulthuis (1981) identified a large area of vegetation on the Prince George Bank as seagrass (Figure 3.1c). Whereas the present study found this vegetation to be macroalgae growing on patches of low profile reef (Figure 2.4b).
Notwithstanding the gaps in the mapping noted above, Bulthuis (1981) concluded that the seagrass areas shown in Figures 3.1a-c had shown little change in its general distribution between 1957 and 1981. The overall seagrass distribution in 2000 remains very similar to that mapped by Bulthuis (1981) and Port Phillip Bay does not appear to have shown the same dramatic variations in total seagrass area or distribution as that observed in Western Port during the 1970’s to 90’s (see Blake and Ball 2001). However, some localised variations in seagrass area and distribution have been observed in Port Phillip Bay during this period and are discussed in the following Section.
While comparisons can be made between the various studies it is important to note that although areas of marine vegetation can readily be observed and drafted/digitised from aerial photography, the differentiation between seagrass and non-seagrass species can only be reliably achieved with an extensive field verification program. It is therefore possible that some of the variations in species and identification of presence of algae may be due to differences in the nature of the field programs undertaken by each study.
Marine and Freshwater Resources Institute – Page 25 Seagrass Mapping of Port Phillip Bay
Figure 3.1a: Seagrass Distribution in Port Phillip Bay, 1957, 1962-63 (Bulthuis 1981). Note: Portarlington to St Leonards was not mapped in these years.
Figure 3.1b: Seagrass Distribution in Port Phillip Bay, 1968-70 (Bulthuis 1981). Note: only the southern part of Swan Bay was mapped in these years.
Marine and Freshwater Resources Institute – Page 26 Seagrass Mapping of Port Phillip Bay
Figure 3.1c: Seagrass Distribution in Port Phillip Bay, 1978-81 (Bulthuis 1981).
Figure 3.1d: Seagrass Distribution in Port Phillip Bay, 2000.
Marine and Freshwater Resources Institute – Page 27 Seagrass Mapping of Port Phillip Bay
Table 3.2 Results of historic studies compared to present study. Report Area Studied Species Species Recorded by Present Comments Recorded Study Willis 1966 Bay-wide H. tasmanica “Z. muelleri/H. tasmanica” Willis considered Z. muelleri Z. muelleri H. australis to be dominant. H. australis A. antarctica A. antarctica Bulthuis 1981 Bay-wide H. tasmanica “Z. muelleri/H. tasmanica” Bulthuis considered H. Z. muelleri H. australis tasmanica to be dominant. H. australis A. antarctica A. antarctica Hope Black 1971 Capell Sound Z. muelleri “Z. muelleri/ H. tasmanica” It is possible that in this report, Eastern Bellarine Peninsula H. australis H. australis A. antarctica is supposed to be Swan Bay A. antarctica H. tasmanica. Corio Bay King et al. 1971 Bay-wide intertidal zone Z. muelleri “Z. muelleri/H. tasmanica” Species identification was later A. antarctica A. antarctica clarified by Shepherd and R. tuberosa Robertson 1989. L. marina Marine Science & Point Lonsdale Bight A. antarctica A. antarctica Whilst the present study only Ecology 1997 H. tasmanica “Z. muelleri/ H. tasmanica” recorded mixed Z. muelleri/H. H. australis tasmanica it is most likely to only have been H. tasmanica here.
Marine and Freshwater Resources Institute – Page 28 Seagrass Mapping of Port Phillip Bay
Kerr 1983 Swan Bay and Queenscliff H. tasmanica “Z. muelleri/ H. tasmanica” Denning et al. 1986 Harbour Z. muelleri H. australis H. australis L. cylindrocarpa Ruppia spp. Dept. of Cons. and Swan Bay and Queenscliff H. tasmanica “Z. muelleri/ H. tasmanica” Environment 1991 Harbour Z. muelleri H. australis H. australis L. marina R. maritima R. tuberosa Ball & O’Callaghan Swan Bay and Queenscliff H. tasmanica “Z. muelleri/ H. tasmanica” 1997 Harbour Z. muelleri H. australis Brown et al. 1980 Corio Bay H. tasmanica “Z. muelleri/ H. tasmanica” H. australis H. australis Marine Science & Corio Bay H. tasmanica “Z. muelleri/ H. tasmanica” H. tasmanica was the primary Ecology 1998 H. australis H. australis species targeted by the MSE study. Brown et al. 1980 Werribee to Point Cook H. tasmanica “Z. muelleri/ H. tasmanica” Brown stated seagrass was generally rare here Watson 1987 St. Kilda Harbour H. tasmanica “Z. muelleri/ H. tasmanica” Watson described 2 discrete permanent beds. Greilach et al. 1998 St. Kilda Harbour H. tasmanica “Z. muelleri/ H. tasmanica” Brighton Boat Harbour Sandringham Boat Harbour Parry & Collett Rosebud-Rye Foreshore H. tasmanica “Z. muelleri/ H. tasmanica” 1985
Marine and Freshwater Resources Institute – Page 29 Seagrass Mapping of Port Phillip Bay
3.3 Assessment of Seagrass Changes from Historical Aerial Photography
A quantitative assessment of historical aerial photography was undertaken by Jenkins et al. (2000) at selected sites in Port Phillip Bay in order to identify changes in seagrass distribution. The results of this study have been summarised here to provide further information about the pattern of changes in seagrass distribution in recent times and to allow comparisons between the past and present distribution.
3.3.1 Selection of Study Sites and Aerial Photography
The study sites selected by Jenkins et al. (2000) represented areas that were known to be important settlement habitats for King George whiting larvae and where variations in seagrass distribution had occurred over time. These sites were located at:
· Grassy Point · Sands Caravan Park, Leopold · Altona · Blairgowrie
Jenkins et al. (2000) also examined a site at Clifton Springs, but as much of the earlier photography for this site (1962-1978) was of a relatively poor resolution, this site has not been considered in this report.
In order to identify the available historical aerial photography for the above study sites, a search was undertaken utilising the aerial photograph database maintained by the Central Plan Office (CPO) of the Office of the Surveyor General. Aerial photography run map index sheets for the region were also checked to ensure that all the available photographs had been identified.
The historical aerial photography utilised for each study site by Jenkins et al. (2000) are summarised in Table 3.3. The actual photography available for each site varied and many of the available photographs could not be used as they were unsuitable for assessing seagrass distribution due to high levels of sun-glare, high tides, poor water clarity and/or poor photography resolution.
3.3.2 Scanning and Geo-registration of Historical Aerial Photography
Contact prints of the historical photography were converted to a digital Tagged Image File Format (TIFF) with a flatbed digital scanner. For the purposes of this study a nominal pixel size of 1 m2 was selected for the digital images. As the aerial photographs were at different scales, the scanning resolution was varied for each photograph to provide the required output of a 1 m pixel width by using the following formula (see NGIS et al. 1998):
scale of aerial photograph x 0.0254 scanning resolution (dpi) = pixel width (m)
Marine and Freshwater Resources Institute – Page 30 Seagrass Mapping of Port Phillip Bay
The scanned TIFF images were imported to the image processing software ER Mapper and geo-registered with ground control points. Ground control points generally consisted of road intersections and real world coordinates were determined from the 1:25,000 State Digital Map Base Topographic Road Layer.
The geo-registered images were cropped to the boundaries of the relevant study areas. An unsupervised classification was then run in ER Mapper to differentiate the areas of seagrass versus bare sand. The resulting raster cells representing seagrass areas were then converted to vector polygons (lines) and imported to ArcView via ArcInfo. An area value for the total area of seagrass within each of the study sites was then calculated in ArcView (Table 3.3).
3.3.3 Results
A selection of the historical photography from each of the study sites is presented in Appendix 2 (Photos 3.1–3.4). The study sites within each image are indicated by a yellow box. The images presented in Appendix 2 represent the years at each site with the highest and lowest cover of seagrass, 1993 (a year in which consistent photography existed for every site) and 2000 (photography from the current mapping). Table 3.3 presents the total seagrass areas derived from the historic photography and site percentage cover values (area of seagrass relative to total area of study site). Figures 3.2a–d show the variations in the percentage cover of seagrass at each study site.
3.3.4 Observations from Historical Aerial Photography
Grassy Point The Grassy Point site is a narrow band (approximately 100-150 m wide) in the nearshore zone and is traversed by two sand bars running parallel to the shore. Most of the seagrass at this site was observed growing in the swale between the sandbars.
From Photographs 3.1a-d it can be seen that most of the seagrass at the Grassy Point site could be observed at the northern half of the study site. Of the years assessed 1947 was the year with the highest percentage cover of seagrass (34.92%, Figure 3.2a), representing a total area of 60,339 m2 (Table 3.3). 1975 was the year with the lowest percentage cover (9.48%), representing an area of 16,383 m2.
It would appear that seagrass cover at the Grassy Point site has followed a pattern of regular fluctuations in area between 1975 and 2000 with the seagrass cover varying by up to 50% (Figure 3.2a). Unfortunately the photography for the period between 1947 and 1974 was unsuitable for assessing seagrass coverage which leaves a large gap in the dataset, particularly as 1947 was the year in which the highest cover of seagrass was recorded. The seagrass cover in 2000 is at the lower end of the apparent cycle of regular fluctuations in seagrass cover at the site.
Marine and Freshwater Resources Institute – Page 31 Seagrass Mapping of Port Phillip Bay
Sands Caravan Park, Leopold The Sands Caravan Park site forms part of an almost continuous band of seagrass on the southern shores of the Geelong Arm that typically extends from Point Richards to Stingaree Bay. The site encompasses seagrass beds in the nearshore zone with seagrass usually also extending further offshore from the seaward boundary of the site.
The distribution of seagrass at the Sands Caravan park site appears to have been relatively even across the entire site (Photographs 3.2a-d). Of the years assessed, 1984 was the year with the highest percentage cover of seagrass (71.06%, Figure 3.2b), with a total area of 148,611 m2 being covered (Table 3.3). 1974 was the year with the lowest percentage cover (8.92%), representing an area of 18,665 m2 and the seagrass cover in this year was much less than that of all the other years (Figure 3.2b).
It can be seen from Figure 3.2b that during the 1970’s and 1980’s there have been large declines and subsequent recoveries in the cover of seagrass at this site. The most significant decrease in seagrass cover occurred between 1970 and 1974 when 80% of the seagrass disappeared (Photo 3.2a). The following ten-year period saw a dramatic increase in seagrass cover with 1984 having the highest area recorded (148,611 m2) and representing approximately eight times the area present in 1974. By 1985 this area had again decreased to 57,647 m2, a decrease in area of approximately 60%. Since 1985 the area of seagrass cover has been relatively stable with an apparent gradual increase in the area covered by seagrass during this period.
Altona The Altona site is almost circular in shape with its southern boundary being formed by a crescent of rocky reef partly exposed at low tide.
Figure 3.2c shows the variation in seagrass cover at the Altona study site. Of the years assessed, 1979 was the year with the highest percentage cover of seagrass (62.08%, Figure 3.2c), with a total area of 93,863 m2 (Table 3.3). 1962 was the year with the lowest percentage cover (12.25%), representing an area of 18,526 m2.
As with the Sands Caravan Park site there have been relatively large variations in the seagrass cover at the Altona site. The seagrass cover was relatively low from 1956 to 1968 but had increased significantly by 1968 and continued to increase up to 1974. A decrease of almost 50% occurred between 1974 and 1975 with a subsequent recovery in area by 1977. From 1974 to 2000 the overall percentage cover of seagrass remained relatively high with pronounced declines and subsequent recoveries in 1975, 1991 and 1997.
Blairgowrie The Blairgowrie site is characterised by extensive shallow sand bars with the seagrass beds being restricted to a narrow band (approximately 150 m wide) in the nearshore zone. The site is bounded by a wide band of bare sand bars on its seaward boundary.
Figure 3.2d shows the variation in seagrass cover at the Blairgowrie study site. Of the years assessed, 1996 was the year with the highest percentage cover of seagrass (43.22%, Figure 3.2d) with a total area of 94,783 m2 (Table 3.3). 1966 was the year with the lowest percentage cover (0.96%), representing an area of only 2,106 m2.
Marine and Freshwater Resources Institute – Page 32 Seagrass Mapping of Port Phillip Bay
Blairgowrie was the site with the highest number of suitable historic photographs for assessment of seagrass cover. As a result the plot in Figure 3.2d enables a pattern of gradual increase in the cover of seagrass since the 1950’s to be observed. From 1957 to around 1971 the percentage cover of seagrass was consistently low, but an increase in area commenced around 1971 which continued up to 1996 when the largest area of cover was recorded. Since 1996 there has been a decline in area, but the 2000 area is still similar to that recorded during most of the late 1980’s and is above the average cover for the entire study period.
3.3.5 Summary of Observations from Historical Aerial Photography
From the historical photography available for the four study sites (Photographs 3.1– 3.4) it is clear that the cover of seagrass at localised areas in Port Phillip Bay can vary greatly over short periods of time (Figures 3.2a-d). At the same time these variations do not appear to follow any definite Bay-wide patterns. A relative seagrass decline at one site could occur at the same time that an increase was observed at another site and vice versa (eg. Blairgowrie and Altona sites 1993 & 1996 ). However, the absence of data for the 1960’s at Grassy Point and the availability of only one record for the 1970’s at the Sands Caravan Park does partly restrict the identification of any Bay- wide patterns
The increase in seagrass cover observed at the Blairgowrie site between 1971-1996 (Figure 3.2d) is consistent with that observed by Parry and Collett (1985) in the nearby Rosebud-Rye nearshore area during 1960-81 outlined previously. Whether or not the changes in seagrass at this site are due to the same influences as observed by Parry and Collett (1985) is difficult to determine from an examination of aerial photography alone, but these localised influences on seagrass cover may in part explain the absence of a Bay-wide pattern of changes.
Altona and Blairgowrie experienced their lowest areas of seagrass cover during the 1960’s while Grassy Point and Sands Caravan Park recorded their lowest areas during the 1970’s (although it should be noted that no suitable photography was available for the 1960’s at Grassy Point). All the sites recorded relatively large declines in seagrass area in either 1974 or 1975, with the exception of Blairgowrie, which may have been subject to localised influences at this time which resulted in an increase in area (see above). Seagrass cover during the 1990’s was generally greater than the 1960’s and 70’s at all the sites, although again there were only limited records for the Grassy Point site for the earlier period.
The seagrass cover in 2000 was above the average area recorded from the historic photography at all of the study sites except for Grassy Point. The seagrass cover at the Sands Caravan Park site in 2000 was the second highest recorded for this site while the seagrass cover at Grassy Point by contrast was the second lowest recorded for this site. At the Altona site the seagrass area recorded in 2000 was higher than any of the areas recorded at this site in the 1960’s, while the seagrass area recorded in 2000 at the Blairgowrie site was higher than the areas recorded at this site in the 1960’s, 70’s and most of the 80’s.
Marine and Freshwater Resources Institute – Page 33 Seagrass Mapping of Port Phillip Bay
Most of the historic aerial photography was flown during the summer months when the angle of the sun is at its optimum for this type of remote sensing. Bulthuis & Woelkerling (1983) recorded a 75% increase in above-sediment biomass of H. tasmanica during spring and summer at Edwards Point, Swan Bay which would seem to suggest that the historic photography was probably flown at a suitable period to observe the peak seagrass cover for each year. The similarity in months between years in which the photography was flown is also likely to have reduced the possible effect of seasonal variations in seagrass cover between years.
3.4. Overview of Assessing Seagrass Changes with Historic Aerial Photography
Assessment of historical aerial photography presents a useful method of identifying broad patterns of seagrass changes in shallow marine environments. However, this study highlighted some of the factors that need to addressed when applying this approach.
Historical aerial photography cannot be ground-truthed and therefore some assumptions need to be made about whether the dark areas visible in the photography represent seagrass, other vegetation and/or reef. Fortunately the study sites utilised by Jenkins et al. (2000) had been subject to field work associated with studies of King George whiting larvae over a number of years and were known to be predominantly vegetated with seagrass when vegetation was present. This combined with the knowledge gained about the sites from field work undertaken as part of this study meant that vegetated areas identified in the historic photography could be reliably classified as seagrass for the purposes of this historic assessment. This highlights the need for fieldwork to be undertaken to provide an understanding of the likely phenomena that may be observed in aerial photographs.
The impact of adverse environmental conditions can limit the usefulness of aerial photographs for studies of seagrass and aquatic substrates. The aerial photography used in this study was typically flown for terrestrial mapping programs, without consideration to conditions suitable for mapping the aquatic environment. Consequently many of the available historical photographs were not suitable. The main reasons for this included high tides, poor water clarity, high levels of sun glare and excessive surface wind ripples. As a result this type of technique is best suited to shallow sites in protected locations where the likely effect of these limiting factors on the use of historic photography are reduced.
The number of suitable historical photographs available for a study is a limiting factor and can present difficulties in drawing conclusions regarding patterns of change within sites, as well as between sites. However, the techniques applied to historic aerial photography by Jenkins et al. (2000) have provided accurate quantitative values for seagrass cover in areas of Port Phillip Bay for periods when data was previously not available.
Marine and Freshwater Resources Institute – Page 34 Seagrass Mapping of Port Phillip Bay Table 3.3 Historical Aerial Photography used to identify changes in seagrass distribution at study sites in Port Phillip Bay (Jenkins et al. 2000) Grassy Point Sands Caravan Park, Leopold Altona Blairgowrie site area (m2) 172,794 site area (m2) 209,139 site area (m2) 151,201 site area (m2) 219,284
Year Month Seagrass (m2) % Seagrass Seagrass (m2) % Seagrass Seagrass (m2) % Seagrass Seagrass (m2) % Seagrass 2000 March/April 19,904 11.52 137,295 65.65 68,219 45.12 59,649 27.20 1998 October/January 25,591 14.81 121,559 58.12 79,013 52.26 81,973 37.38 1997 April 38,705 22.40 127,339 60.89 29,593 19.57 71,881 32.78 1996 March 74,013 48.95 94,783# 43.22# 1993 January 27,112 15.69 97,363 46.55 92,353 61.08 54,292 24.76 1992 July/August 51,243 33.89 71,664 32.68 1991 April/June 78,719 52.06 56,846 25.92 1990 January/March 33,394 19.33 124,021 59.30 61,124 27.87 1989 November 64,271 29.31 1987 January 41,980 19.14 1985 December 57,647 27.56 29,081 13.26 1984 February/May 43,770 25.33 148,611# 71.06# 1982 October/Nov. 71,273 47.14 27,260 12.43 1981 January 43,087 19.65 1979 January 93,863# 62.08# 28,919 13.19 1978 December 39,470 22.84 1977 September 77,647 51.35 18,112 8.26 1975 March 16,383* 9.48* 44,892 29.69 27,843 12.70 1974 November 26,087 15.10 18,665* 8.92* 86,972 57.52 25,751 11.74 1972 January 59,814 39.56 15,833 7.22 1971 December 12,024 5.48 1970 December 94,043 44.97 1968 October/December 19,917 13.17 26,621 12.14 1966 February/April 67,255 32.16 33,768 22.33 2,106* 0.96* 1962 January/February 90,442 43.24 18,526* 12.25* 19,592 8.93 1961 July 12,015 5.48 1960 February 19,364 12.81 1959 December 12,274 5.60 1957 January 23,189 10.57 1956 Not stated 23,752 15.71 1947 Not stated 60,339# 34.92# Average 33,076 19.14 98,567 47.13 56,830 37.59 39,287 17.92 *Year with the lowest seagrass cover #Year with the highest seagrass cover Marine and Freshwater Resources Institute – Page 35 Seagrass Mapping of Port Phillip Bay
% Seagrass Cover at Grassy Point
100
90
80
70
60
50
40
% Seagrass Cover 30
20
10
0 1940 1950 1960 1970 1980 1990 2000 Year
Figure 3.2a Area of seagrass cover as a percentage of total study area at Grassy Point (after Jenkins et al. 2000).
% Seagrass Cover at Sands Caravan Park, Leopold
100
90
80
70
60
50
40
% Seagrass Cover 30
20
10
0 1940 1950 1960 1970 1980 1990 2000 Year
Figure 3.2b Area of seagrass cover as a percentage of total study area at Sands Caravan Park site, Leopold (after Jenkins et al. 2000).
Marine and Freshwater Resources Institute – Page 36 Seagrass Mapping of Port Phillip Bay
% Seagrass Cover at Altona
100
90
80
70
60
50
40
% Seagrass Cover 30
20
10
0 1940 1950 1960 1970 1980 1990 2000 Year
Figure 3.2c Area of seagrass cover as a percentage of total study area at Altona (after Jenkins et al. 2000).
% Seagrass Cover at Blairgowrie
100
90
80
70
60
50
40
% Seagrass Cover 30
20
10
0 1940 1950 1960 1970 1980 1990 2000 Year
Figure 3.2d Area of seagrass cover as a percentage of total study area at Blairgowrie (after Jenkins et al. 2000).
Marine and Freshwater Resources Institute – Page 37 Seagrass Mapping of Port Phillip Bay
4. GENERAL DISCUSSION AND FINDINGS
The present study mapped 169.4 km2 of seagrass, macroalgae and Pyura in Port Phillip Bay, of which 67.99 km2 (40%) was seagrass or a mixture of seagrass and macroalgae.
The category of “Zostera/Heterozostera” (representing a mix of Zostera muelleri and Heterozostera tasmanica) was the most common category of seagrass recorded in the Bay. Zostera/Heterozostera as monospecific beds or mixed with other species covered 64.53 km2 (95% of the total seagrass area).
The majority of Zostera/Heterozostera was recorded in Swan Bay and along the southern shores of the Geelong Arm and Corio Bay. Significant areas were also recorded along the northern shores of Corio Bay and the Geelong Arm, south of St. Leonards (West Sand Bank), around Mud Islands (Great Sand), offshore from Sorrento (South Sand) and along the Rosebud to Blairgowrie foreshore. Smaller isolated patches are scattered around Port Phillip Bay, with very little being present along the eastern shores.
The other species of seagrass recorded in Port Phillip Bay were Amphibolis antarctica and Halophila australis. A. antarctica covered an area of 2.09 km2 (3% of total seagrass area) and was restricted in its distribution to The Heads region encompassing Point Lonsdale Bay, north to Queenscliff Pier, and along the shore from Point Nepean to Sorrento. H. australis was the least common species recorded, accounting for the remaining 2% of seagrass mapped in Port Phillip Bay. Its distribution was restricted to the deeper softer sediments of Swan Bay, the Geelong Arm and Corio Bay.
The present survey did not record any occurrences of the species Ruppia tuberosa, Ruppia maritima, Lepilaena marina or Lepilaena cylindrocarpa which have previously been recorded in Swan Bay (DCE 1991, Kerr 1983 and King et al. 1971). This should not be seen as an indication that these species are not present in Swan Bay, or elsewhere in Port Phillip Bay, as these species could have occurred in patches that were too small to be mapped by the present study or may have been hidden by the dominant stands of Zostera/Heterozostera. It would appear that a fine-scale survey of Swan Bay would be required to determine the presence and distribution of these species.
Bulthuis (1981) concluded that there had been little change in the general distribution of seagrass in Port Phillip Bay between 1957 to 1981. The results of the present mapping survey show a similar seagrass distribution pattern to those produced by Bulthuis (1981) for 1978-81. However, site-specific changes in seagrass distribution have occurred in the Bay, such as the marked increase in the distribution of H. tasmanica along the Rosebud-Rye foreshore between 1960 and 1981 (Parry and Collett 1985).
A quantitative assessment of changes in seagrass distribution from historical aerial photography highlighted a pattern of relatively frequent small-scale changes at localised sites. It would appear from the assessment of historic photography at the four study sites spread around Port Phillip Bay that, with exception of the Blairgowrie
Marine and Freshwater Resources Institute – Page 38 Seagrass Mapping of Port Phillip Bay site, the area of seagrass cover in 2000 was greater than the average yearly cover of seagrass recorded at these sites since the 1950’s.
The present mapping survey combined with a review of historical mapping projects, other historic research and a review of historical photography indicate that the overall seagrass distribution in Port Phillip Bay has remained relatively constant since 1957. Port Phillip Bay does not appear to have experienced the same dramatic Bay-wide changes in seagrass cover experienced in Western Port during the late 1970’s to early 80’s. However, whilst the general distribution may be relatively constant, the actual cover of seagrass at specific sites can fluctuate significantly over short periods of time.
ACKNOWLEDGMENTS
This study was commissioned by Fisheries Victoria and Parks, Flora and Fauna and coordinated by John Garnham, Don Hough and Laurie Ferns. Penny Morris undertook most of the aerial photography interpretation and digital capture of seagrass polygons. All fieldwork was conducted by Sean Blake and Brett Abbott.
The palm-top system for recording DGPS and habitat information was developed by Brett Mathews at MAFRI. Joe Leach of the Department of Geomatics, University of Melbourne facilitated use of the specialised survey vessel “Korrong”.
Marine and Freshwater Resources Institute – Page 39 Seagrass Mapping of Port Phillip Bay
REFERENCES
Ball, D. and O’Callaghan, P. (1997). Queenscliff Harbour Environmental Values Study. Report for Parks Victoria by the Marine & Freshwater Resources Institute, Queenscliff, Vic.
Bird, E.C.F. (1993). The Coast of Victoria the Shaping of Scenery. Melbourne University Press 1993.
Black, K.P., Hatton, D. and Rosenberg, M. (1993). Locally and Externally-Driven Dynamics of a Semi-Enclosed Bay in Southern Australia. Journal of Coastal Research,: 9: 509-538.
Blake, S., Roob, R., Patterson, E. (2000). Seagrass Mapping of Victoria’s Minor Inlets. Report by the Marine and Freshwater Resources Institute, Queenscliff, Victoria.
Blake, S. & Ball, D. (2001). Victorian Marine Habitat Database Seagrass Mapping of Western Port. Report by the Marine and Freshwater Resources Institute, Queenscliff, Victoria.
Brown, V.B., Rowan, K.S. and Ducker, S.C. (1980). The Effects of Sewage Effluent on the Macrophytes off Werribee, Port Phillip Bay. Ministry of Conservation Victoria, Environmental Studies Program, Task Report No. 273, pp. 233-238.
Brown, V.B. (Undated). A Seagrass Thrives in a Eutrophic Environment. Helobiae Newsletter. No. 2, pp. 6-8.
Bulthuis, D.A. (1981). Distribution of Seagrasses in Port Phillip Victoria. Technical Report No.5. Ministry for Conservation. Marine Science Laboratories.
Bulthuis, D.A., Axelrad, D.M. and Mickleson, M.J. (1992). Growth of the Seagrass Heterozostera tasmanica Limited by Nitrogen in Port Phillip Bay, Australia. Marine Ecology Progress Series. 89: 269-275.
Bulthuis, D.A. and Woelkerling, W.J. (1983). Seasonal Variation in Standing Crop, Density and Leaf Growth Rate of the Seagrass, H. tasmanica, in Western Port and Port Phillip Bay, Victoria. in: Studies on the Seagrass, H. Tasmanica, in Western Port and Port Phillip Bay, Vic. Aust, 1982. Marine Science Labs.
Denning, N.T., Hudson, H.A., Kerr, E.A. and Strother, S. (1986). Distribution of Vascular Hydrophytes and Description of Associated Macrofaunal Communities in Swan Bay, Victoria. Proc. Roy. Soc. Vict. 98(4): 139-145.
Department of Conservation & Environment (1991). Swan Bay Marine and Wildlife Reserves. Proposed Management Plan. Department of Conservation & Environment.
Edgar, G.J. (1997). Australian Marine Life - the Plants and Animals of Temperate Waters. Reed Books, Kew, Victoria.
Marine and Freshwater Resources Institute – Page 40 Seagrass Mapping of Port Phillip Bay
Fisheries Victoria (1998). Catch and Effort Information Bulletin. Produced by Natural Resources and Environment and Marine and Freshwater Resources Institute.
Ferns, L. & Hough, D. (1999). Environmental inventory of Victoria's marine ecosystems : Stage 3 (Vol. 1) : final report. Lawrance Ferns, Don Hough (editors). Dept. of Natural Resources and Environment, 1999
Greilach, P., Ball, D., Coleman, N., Brady, B., Hamer, P., O’Callaghan, P. and Morris, P. (1998). St. Kilda Harbour Environment Values Assessment. A Report for Parks Victoria, by the Marine & Freshwater Resources Institute, Queenscliff, Victoria.
Harris, G., Bateley, G., Fox, D., Hall, D., Jernakoff, P., Molloy, R., Murray, A., Newell, B., Parslow, J., Skyring, G. and Walker, S. (1996). Port Phillip Bay Environmental Study Final Report. CSIRO, Canberra, Australia, 1996, p.239.
Hastings, K (1995) Assessing Seagrass Change Off Western Australia, GIS Asia Pacific.
Hope Black, J. (1971). Benthic Communities. Memoirs of the National Museum of Victoria, Melbourne. Vol. 32, pp. 129-170.
Jenkins, G.P., Watson, G.F., Hammond, L.S. (1993). Patterns of Utilisation of Seagrass (Heterozostera) Dominated Habitats as Nursery by Commercially Important Fish. Technical Report no. 19. Victorian Institute of Marine Sciences, 1993.
Jenkins, G.P., Wheatley, M.J. and Poore, A.G.P. (1996). Spatial Variation in Recruitment, Growth and Feeding of Post-settlement King George whiting, Sillaginodes punctata, Associated with Seagrass Beds of Port Phillip Bay, Australia. Can. J. Fish. Aquat. Sci. 53: 350-359.
Jenkins, G.P., May, H.M.A. Wheatley, M.J. and Holloway, M.G. (1997) Comparison of fish assemblages associated with seagrass and adjacent unvegetated habitats of Port Phillip Bay and Corner Inlet, Victoria, Australia, with emphasis on commercial species. Estuarine, Coastal & Shelf Science 44: 569-588.
Jenkins, G.P. and Wheatley, M.J. (1998). The Influence of Habitat Structure on Nearshore Fish Assemblages in a Southern Australian Embayment: Comparison of Shallow Seagrass, Reef-algal and Unvegetated Sand Habitats, with Emphasis on their Importance to Recruitment. Journal of Experimental Marine Biology and Ecology 221: 147-172.
Jenkins, G.P., Hatton, D. and Black, K. (2000) Environmental Determinants of Recruitment Success of King George Whiting. Marine and Freshwater Resources Institute report to Fisheries Research and Development Corporation Project No. 98/141, November 2000.
Marine and Freshwater Resources Institute – Page 41 Seagrass Mapping of Port Phillip Bay
Jones, I. (1980). Tidal and Wind-Driven Currents in Bass Strait. Australian J. Marine Freshwater Research, 31: 109-17.
Keble, R.A. (1946). The Sunklands of Port Phillip and Bass Strait. Memoirs of the National Museum of Victoria. 14: 69-122.
Kerr, E.A. (1983). The Distribution of Seagrass in Swan Bay. Geel. Nat. Vol 19: 59- 73.
Kerr, E.A. (1986). The Ecology and Ecophysiology of Zostera muelleri in Swan Bay, Victoria. PhD Thesis, Deakin University, Victoria.
Kerr, E.A. and Strother, S. (1990). Seasonal Changes in the Standing Crop of Zostera muelleri in south-eastern Australia. Aquatic Botany. No. 38, pp. 369-376.
King, R.J., Hope Black, J. and Ducker, S.C. (1971). Intertidal Ecology of Port Phillip Bay with Systematic Lists of Plants and Animals. Memoirs of the National Museum of Victoria, 32: 93-128.
Light, B.R. and Beardall, J. (1998). Distribution and Spatial Variation of Benthic Microalgal Biomass in a Temperate, Shallow-Water Marine System. Aquatic Botany 61: 39-54.
Light, B.R. and Woelkerling, J. (1992). Literature and Information Review of the Benthic Flora of Port Phillip Bay, Victoria, Australia. Technical Report No. 6. CSIRO Port Phillip Bay Environmental Study.
Lloyd, D. (1997) Ocean Rescue 2000 - Sea Notes - Seagrass. Environment Australia.
Marine Science and Ecology Pty. Ltd. (1997). Report on Seabed Survey of the Lonsdale Bight. Marine Science and Ecology Pty. Ltd
Marine Science & Ecology Pty. Ltd. (1998). VCA Channel Improvement Program Monitoring Program. Final Report on Seagrass Monitoring. Marine Science and Ecology Pty. Ltd.
National Geographic Information Systems (Australia) Pty Ltd, University of Western Australia Botany Department and D.A. Lord & Associates Pty Ltd (1998) Changes in Seagrass Coverage on Success and Parmelia Banks Between 1965 and 1995. Report to Cockburn Cement Limited, April 1998.
Parry, G.D. and Collett, L.C. (1985). The Control of Seagrass in the Rosebud-Rye Region of Port Phillip Bay. Coastal Unit Technical Report No.2. Ministry for Planning and Environment.
Robertson, E.L. (1984). Seagrasses, in Womersley, H.B.S. (1984). The Marine Benthic Flora of Southern Australia. Part I. D.J. Woolman, Government Printer, South Australia.
Marine and Freshwater Resources Institute – Page 42 Seagrass Mapping of Port Phillip Bay
Roob, R. and Ball, D. (1997) Victorian Marine Habitat Database, Seagrass, Gippsland Lakes. A report for Fisheries Victoria, DNRE. The Marine and Freshwater Resources Institute, Queenscliff, Victoria.
Roob, R., Morris, P. and Werner, G. (1998) Victorian Marine Habitat Database, Seagrass, Corner Inlet and Nooramunga. Marine and Freshwater Resources Institute Report No. 12, Queenscliff, Victoria.
Saenger, P. and Bucher D. (1989). An Inventory of Australian Estuaries and Enclosed Marine Waters. Database – Victoria: The Entire Coastline. Australian National Parks and Wildlife Service Unpublished Consultancy Report.
Saunders, T. (1997). The Influence of Water Depth and Habitat Complexity on Fish Communities Associated with Seagrass in Swan Bay, Victoria. BSc Thesis, Dept. Zoology, University of Melbourne.
Seedsman, R.W. and Marsden, M.A.H. (1980). Sediment Distribution and Movement within Corio Bay. Ministry for Conservation, Melbourne. Port Phillip Regional Environmental Study, Environmental Studies Series. No. 312.
Shaw, M. and Jenkins, G.P. (1992) Spatial Variation in Feeding, Prey Distribution and Food Limitation of Juvenile Flounder Rhombosolea tapirina Gunther. Journal of Experimental Marine Biology and Ecology 165: 1-21.
Shepherd, S.A. & Robertson, E.L. (1989). Regional Studies – Seagrasses of South Australia and Bass Strait, in Biology of Seagrasses. A Treatise on the Biology of Seagrasses with Special Reference to the Australian Region. pp 211-229. Aquatic Plant Studies 2, Elsevier, The Netherlands.
Spencer, R.D. (1970). An Ecological Study of the Subtidal Macrophytic Vegetation of three selected areas of Port Phillip Bay: Werribee, Altona and Carrum. Unpublished MSc Thesis, School of Botany, University of Melbourne.
Stephens, A.C. (1995). Seagrass in Western Port, Victoria. Australia. Environment Protection Authority, No. 490. Victoria. Australia.
Victorian Channels Authority (2000). Victorian Channels Authority Web Site, http://www.vicchannels.vic.gov.au.
Victorian Channels Authority (1999). Victorian Channels Authority Annual Report, 1999.
Victorian Government (1992). Caring for Port Phillip Bay Now and Into the Future. Open Space 2000 Program, Victoria.
Victorian Government – Anonymous (1989). Submission by the Government of Victoria to the Federal Parliamentary Inquiry to Review the Protection of the Australian Coastal Environment.
Marine and Freshwater Resources Institute – Page 43 Seagrass Mapping of Port Phillip Bay
Watson, J.E. (1979). Distribution and Ecology of Seagrass Meadows. Consultants Report prepared for Port Bellarine Victoria Environmental Effects Statement, Appendix 8.
Watson, J.E. (1987). Seagrass Beds in St. Kilda Harbour. Report to St. Kilda City Council. Marine Science & Ecology.
Willis, J.H. (1966). Port Phillip Survey 1957-1963: Vegetation. Memoirs of the National Museum of Victoria. Vol. 27: 119-132.
Winstanley, R. (1995). The State of the Marine Environment Report for Australia, Technical Annex: 3. Environment Australia.
Womersley, H.B.S. (1984). The Marine Benthic Flora of Southern Australia. Part I. Government Printer, South Australia.
Marine and Freshwater Resources Institute – Page 44 Seagrass Mapping of Port Phillip Bay - Appendices
APPENDIX 1 SEAGRASS GIS LAYER METADATA
Marine and Freshwater Resources Institute – Page A1 Seagrass Mapping of Port Phillip Bay - Appendices
Name: PPB_SEAGRS25 Full Name: Port Phillip Bay Seagrass Distribution Spatial Extent: Port Phillip Owner: Department of Natural Resources and Environment Custodian: Department of Natural Resources and Environment Access: Unrestricted Map Input Scale: 1:25,000 Search Words: Seagrass, Estuary, Marine Habitat, Macroalgae, Port Phillip Bay Abstract: PPB_SEAGR25 is a polygon layer defining the spatial extent, species distribution and density of seagrass and macroalgae within Port Phillip Bay mapped in 2000.
Application of Layer: General: PPB_SEAGRS25 is a 1:25,000 layer which represents spatial extent, species distribution and density of seagrass and other aquatic vegetation within Port Phillip Bay. This layer forms part of a baseline survey of seagrass within Victoria. Ecological research into the health of seagrass meadows requires the type of detailed information collected in this baseline survey.
Layer Design Summary: Current Layer Design Considerations: This information represents a “snap-shot” in time of the spatial extent of seagrass meadows in Port Phillip Bay. The area of coverage and density of the various species of seagrass changes with time, both seasonally and yearly.
Future Layer Design Considerations: Future design considerations may include adding extra species and recording the condition of the seagrass in relation to epiphyte coverage.
Summary of Relationship to other Layers: The landward boundary of the layer corresponds to the 1:25,000 coastline (SHORE25). The coastline is subject to change especially in areas subject to erosion or mass movement of coastal sediments and at the entrance to the inlets.
This layer forms part of a State wide program to map seagrass throughout Victoria. Other seagrass layers exist for Gippsland Lakes, Corner Inlet/Nooramunga, Minor Inlets of Eastern Victoria and Western Port.
Data Currency Information: Data Set Status: Complete
Data Collection: Collection Period:
Data Site: Port Phillip Bay Beginning Date: March 2000 Ending Date: December 2000 Update Frequency: Not Planned
Data Format: ArcInfo Coverage
Marine and Freshwater Resources Institute – Page A2 Seagrass Mapping of Port Phillip Bay - Appendices
Projection/Datum: Transverse Mercator (AMG Zone 55) & AGD66
Data Lineage and Quality: Data Set Origin: Originality: Primary Data Collection Method: Remotely Sensed - Aerial Photography Field Measurements
Data Set Source: 1:20,000 Colour Aerial Photography enlarged to a scale of 1:10,000 Photography flown on 25th and 31st March 2000, and 2nd and 3rd of April 2000.
Data Set Processing Details: The delineation of the seagrass meadows was conducted through Aerial Photograph Interpretation. The linework was digitized from stable base overlays plotted on 1:10,000 colour photo prints. Polygons were attributed with species and density from data collected at sample sites in the field (see PPB_SEAGR25 Field Work layers).
Positional Accuracy: Precision: Horizontal accuracy of 5m to 10m. Vertical accuracy NA
Attribute Accuracy: Attributes have been verified by MAFRI.
Completeness: Layer is complete for Port Phillip Bay
Further Information: Authors/Collators: David Ball Penny Morris
Supporting Documentation:
Blake, S. and Ball, D. (2001) Seagrass Mapping of Port Phillip Bay, Marine and Freshwater Resources Institute report to Fisheries Victoria. June 2001
Administration:
Documentation Details: Documenter: David Ball Address: MAFRI, Weeroona Parade, Queenscliff 3225 Position Senior Environmental Scientist
Marine and Freshwater Resources Institute – Page A3 Seagrass Mapping of Port Phillip Bay - Appendices
PPB_SEAGRS25 Polygon Attribute Table
Item Full Coln Item Name Item Out Item Item Notes Name Width Width Type Dec. Internal ID 17 Seagrass25# 4 5 B - User ID 21 Seagrass25-id 4 5 B - Seagrass 25 Class 8 8 I 0 Classification code for Classification seagrass categories. Seagrass 33 Class_desc 100 100 C - Text description of seagrass Classification categories. See table below. description Summarised 133 Map_class 8 8 I 0 Summarised seagrass Seagrass classification codes used in classification map production Summarised 141 Map_text 100 100 C - Text description of Seagrass summarised seagrass Classification classifications used in map description production. See table below Substrate code 241 Sub_type 5 5 C - Substrate type code Substrate 246 Sub_desc 50 50 C - Substrate type text description description Habitat code 296 Hab_code 8 8 I 0 Habitat type code Habitat 304 Hab_desc 50 50 C - Habitat type text description description
Marine and Freshwater Resources Institute – Page A4 Seagrass Mapping of Port Phillip Bay - Appendices
Seagrass and Non-Seagrass Categories
Class Class_desc Map_class Map_text 3 Sparse Zostera/Heterozostera 3 Sparse Zostera/Heterozostera 6 Medium Zostera/Heterozostera 6 Medium Zostera/Heterozostera 9 Dense Zostera/Heterozostera 9 Dense Zostera/Heterozostera 20 Undefined Macroalgae 20 Undefined Macroalgae 51 Sparse Zostera/Heterozostera & Halophila Mix 51 Sparse Zostera/Heterozostera & Halophila Mix 52 Medium Zostera/Heterozostera & Halophila Mix 52 Medium Zostera/Heterozostera & Halophila Mix 97 Bare Reef 97 Bare Reef 98 No Visible Bottom 98 No Visible Bottom 99 Bare Sediment 99 Bare Sediment 100 Land 100 Land 107 Sparse Amphibolis & Undefined Macroalgae Mix 107 Sparse Amphibolis & Undefined Macroalgae Mix 108 Medium Amphibolis & Undefined Macroalgal Mix 108 Medium Amphibolis & Undefined Macroalgal Mix 111 Sparse Amphibolis 111 Sparse Amphibolis 112 Medium Amphibolis 112 Medium Amphibolis 113 Dense Amphibolis 113 Dense Amphibolis 203 Sparse Caulerpa Dominant Macroalgae 600 Caulerpa Dominant Macroalgae 204 Medium Caulerpa Dominant Macroalgae 610 Ulva & Caulerpa Dominant Macroalgae 205 Dense Caulerpa Dominant Macroalgae 212 Phyllospora /Ecklonia Dominant Macroalgae 206 Sparse Ulva & Caulerpa Dominant Macroalgae 650 Codium Dominant Macroalgae 207 Medium Ulva & Caulerpa Dominant Macroalgae 620 Drift Algae 212 Phyllospora /Ecklonia Dominant Macroalgae 301 Sparse Halophila & Filamentous Algae Mix 215 Sparse Codium Dominant Macroalgae 302 Medium Halophila & Filamentous Algae Mix 218 Sparse Drift Algae 303 Dense Halophila & Filamentous Algae Mix 219 Medium Drift Algae 630 Pyura 301 Sparse Halophila & Filamentous Algae Mix 640 Pyura & Macroalgae Mix 302 Medium Halophila & Filamentous Algae Mix 501 Sparse Zostera/Heterozostera & Filamentous Algae Mix 303 Dense Halophila & Filamentous Algae Mix 502 Medium Zostera/Heterozostera & Filamentous Algae Mix 401 Sparse Pyura 503 Dense Zostera/Heterozostera & Filamentous Algae Mix 402 Medium Pyura 504 Sparse Zostera/Heterozostera & Caulerpa Mix 404 Sparse Pyura & Macroalgae Mix 505 Medium Zostera/Heterozostera & Caulerpa Mix 405 Medium Pyura & Macroalgae Mix 507 Sparse Zostera/Heterozostera & Undefined Macroalgae Mix 501 Sparse Zostera/Heterozostera & Filamentous Algae 508 Medium Zostera/Heterozostera & Undefined Macroalgae Mix Mix 502 Medium Zostera/Heterozostera & Filamentous Algae 509 Dense Zostera/Heterozostera & Undefined Macroalgae Mix Mix 503 Dense Zostera/Heterozostera & Filamentous Algae Mix 504 Sparse Zostera/Heterozostera & Caulerpa Mix 505 Medium Zostera/Heterozostera & Caulerpa Mix 507 Sparse Zostera/Heterozostera & Undefined Macroalgae Mix 508 Medium Zostera/Heterozostera & Undefined Macroalgae Mix 509 Dense Zostera/Heterozostera & Undefined Macroalgae Mix
Marine and Freshwater Resources Institute – Page A5 Seagrass Mapping of Port Phillip Bay - Appendices
Name: PPB_SEAGRS25 – Field Work Full Name: Seagrass fieldwork in Port Phillip Bay Spatial Extent: Port Phillip Bay Owner: Department of Natural Resources and Environment Custodian: Department of Natural Resources and Environment Access: Unrestricted Map Input Scale: 1:25,000 Search Words: Seagrass, Marine Habitat, Macroalgae, Port Phillip Bay Abstract: This data consists of twenty seven separate point layers generated from field sampling undertaken in Port Phillip Bay to classify seagrass polygons in the layer PPB_SEAGR25. Three of the layers consist of separate spot samples and twenty four contain the results of continuous transects. Seagrass species, density, substrate and presence of algae were recorded at each sampling point.
Application of Layer: General: PPB_SEAGR25 is a 1:25,000 layer representing the spatial extent, species distribution and density of seagrass meadows in Port Phillip Bay. In order to classify the polygons interpreted from aerial photography, fieldwork was conducted throughout Port Phillip Bay to identify seagrass presence, species, density and substrate type. Fieldwork was undertaken in the form of firstly; continuous transects recorded digitally on-board a specialised survey vessel with a submersible pod featuring glass-bottomed observation points for use in deeper areas with good water clarity and secondly; spot samples recorded by an observer in a small punt for the shallow areas.
The respective layers for the spot samples and continuous transects are as follows:
Shapefile Location of Fieldwork
Spot Samples Swan Bay east.shp The Eastern side of Swan Bay Miscellaneous points.shp Points throughout Port Phillip Bay Corio Quay points.shp Points in Corio Bay
Continuous Transects Sorrento to Point Nepean.shp Sorrento to Point Nepean Rye to Sorrento.shp Rye to Sorrento Sands Region.shp Sands Region Dromana to Rosebud.shp Dromana to Rosebud Mornington to Dromana.shp Mornington to Dromana Frankston to Mornington.shp Frankston to Mornington Beaumaris to Frankston.shp Beaumaris to Frankston Sandringham to Beaumaris.shp Sandringham to Beaumaris Williamstown to Sandringham.shp Williamstown to Sandringham Point Cook to Williamstown.shp Point Cook to Williamstown Werribee to Point Cook.shp Werribee to Point Cook Kirk Point to Werribee.shp Kirk Point to Werribee Pt Wilson to Kirk Point.shp Point Wilson to Kirk Point Avalon to Pt Wilson.shp Avalon to Point Wilson Shell Refinery to Avalon.shp Shell Refinery to Avalon Smorgys to Shell Refinery.shp Smorgys to Shell Refinery Stingaree Bay to Smorgys.shp Stingaree Bay to Smorgys Clifton Springs to Stingaree Bay.shp Clifton Springs to Stingaree Bay Portarlington to Clifton Springs.shp Port Arlington to Clifton Springs
Marine and Freshwater Resources Institute – Page A6 Seagrass Mapping of Port Phillip Bay - Appendices
Indented Heads to Portarlington.shp Indented Heads to Portarlington Swan Bay to Indented Heads.shp Swan Bay to Indented Heads Swan Bay North.shp Swan Bay North Swan Bay South.shp Swan Bay South Point Lonsdale to Swan Bay.shp Point Lonsdale to Swan Bay
Layer Design Summary: Current Layer Design Considerations: This information represents a “snap-shot” in time of the status of seagrass and other aquatic vegetation in Port Phillip Bay at the time of the field surveys. The coverage and density of the various species of seagrass and algae changes with time, both seasonally and yearly.
Summary of Relationship to other Layers: The sample sites were surveyed to classify seagrass polygons in the layer PPB_SEAGRS25. This layer forms part of a Statewide program to map seagrass throughout Victoria. Other seagrass layers exist for Gippsland Lakes, Corner Inlet/Nooramunga, Minor Inlets of Eastern Victoria and Western Port.
Data Currency Information: Data Set Status: Complete
Data Collection: Collection Period:
Data Site: Port Phillip Bay Beginning Date: May 2000 Ending Date: December 2000 Update Frequency: Not Planned
Data Format: ESRI ArcView Shapefiles
Projection/Datum: Transverse Mercator (AMG Zone 55) & AGD66
Data Lineage and Quality: Data Set Origin: Originality: Primary Data Collection Method: Field Measurements by Observer with DGPS.
Data Set Source: Data was collected in the field by MAFRI scientists between May and December 2000.
Data Set Processing Details: Data was collected using a differential GPS and observations at each site were recorded on field sheets for each spot sample and subsequently entered to a spreadsheet. Transect data was recorded to a palm-top computer linked to a DGPS with pre-defined "hot-keys" for species type, density and substrate. Data was downloaded to a PC, verified and then attributed with text descriptions. All data was imported to ArcView and then converted to a Shapefile format.
Positional Accuracy: Precision: Horizontal accuracy of 5m to 10m. Vertical accuracy NA
Marine and Freshwater Resources Institute – Page A7 Seagrass Mapping of Port Phillip Bay - Appendices
Attribute Accuracy: Attributes have been verified by MAFRI.
Completeness: Layers are complete for Port Phillip Bay
Further Information: Authors/Collators: David Ball Penny Morris Sean Blake
Supporting Documentation:
Blake, S and Ball, D. (2001) Seagrass Mapping of Port Phillip Bay, Marine and Freshwater Resources Institute Report No. 39, June 2001.
Administration:
Documentation Details: Documenter: David Ball Address: MAFRI, Weeroona Parade, Queenscliff 3225 Position Senior Environmental Scientist
Marine and Freshwater Resources Institute – Page A8 Seagrass Mapping of Port Phillip Bay - Appendices
PPB_SEAGRS25 Fieldwork Shapefile Point Attributes
Item Full Name Item Name Item Item Notes Type Dec. Latitude Latitude N 6 Decimal degrees Longitude Longitude N 6 Decimal degrees Abundance/Density Ab_su_code N 0 Codes for seagrass density or substrate type code where site was bare (see below). Abundance/Density Abundance C - Description for seagrass density or substrate type description where site was bare (see below). Species type code Spp_code C - Codes for seagrass categories. See table below Species type Species C - Description of seagrass categories. See table description below Site Location Location C - Location description of site surveyed Observations Observatio C - Any observations made at the site Observer Observer C - MAFRI scientist making observations Survey Date Date N 0 Date of survey observations
Abundance/Density and Substrate Categories Recorded in Field Surveys
Ab_su_code Abundance/Density and Substrate Categories 1 Sediment 2 Low Profile Reef 3 High Profile Reef 5 Sparse 6 Medium 7 Dense 98 No Visible Bottom
Seagrass and Macroalgae Categories Recorded in Field Surveys
Spp_code Seagrass/Macroalgae Species A Zostera/Heterozostera B Ulva & Caulerpa mix C Caulerpa D Zostera/Heterozostera & Halophila mix E Zostera/Heterozostera & filamentous algae mix F Halophila & filamentous algae mix G Undefined filamentous subtidal vegetation H Undefined macroalgal subtidal vegetation I Zostera/Heterozostera & Caulerpa mix J Zostera/Heterozostera & undefined macroalgal mix K Amphibolis L Ecklonia dominant M Phyllospora/Ecklonia dominant P Pyura Q Pyura & Algae mix R Bare Reef S Bare Sediment T No Visible Bottom X Codium Z Drift Algae
Marine and Freshwater Resources Institute – Page A9 Seagrass Mapping of Port Phillip Bay - Appendices
APPENDIX 2 PORT PHILLIP BAY HISTORICAL AERIAL PHOTOGRAPHY
IN ORDER TO REDUCE THE SIZE OF THIS FILE THE AERIAL PHOTOGRAPHY FROM THIS APPENDIX HAS BEEN EXTRACTED TO THE FILE:
PPB HISTORIC PHOTOGRAPHY.PDF
File is located in the Fishing and Aquaculture theme at www.nre.vic.gov.au
Marine and Freshwater Resources Institute – Page A10 Seagrass Mapping of Port Phillip Bay - Appendices
APPENDIX 3 PORT PHILLIP BAY SEAGRASS MAPS
IN ORDER TO REDUCE THE SIZE OF THIS FILE THE MAPS FROM THIS APPENDIX HAVE BEEN EXTRACTED TO THE FILES:
PPB MAPS A.PDF & PPB MAPS B.PDF
Files are located in the Fishing and Aquaculture theme at www.nre.vic.gov.au
Marine and Freshwater Resources Institute – Page A19